TaitNet P25 conventional networks. System Manual

Transcription

1 TaitNet P25 conventional networks System Manual MBA Issue 5 January 2009

2 Contact Information Tait Radio Communications Corporate Head Office Tait Electronics Limited P.O. Box 1645 Christchurch New Zealand For the address and telephone number of regional offices, refer to the TaitWorld website: Website: Technical Support For assistance with specific technical issues, contact Technical Support: Website: Copyright and Trademarks All information contained in this document is the property of Tait Electronics Limited. All rights reserved. This document may not, in whole or in part, be copied, photocopied, reproduced, translated, stored, or reduced to any electronic medium or machine-readable form, without prior written permission from Tait Electronics Limited. The word TAIT and the TAIT logo are trademarks of Tait Electronics Limited. All trade names referenced are the service mark, trademark or registered trademark of the respective manufacturers. Disclaimer There are no warranties extended or granted by this document. Tait Electronics Limited accepts no responsibility for damage arising from use of the information contained in the document or of the equipment and software it describes. It is the responsibility of the user to ensure that use of such information, equipment and software complies with the laws, rules and regulations of the applicable jurisdictions. Enquiries and Comments If you have any enquiries regarding this document, or any comments, suggestions and notifications of errors, please contact Technical Support. Updates of Manual and Equipment In the interests of improving the performance, reliability or servicing of the equipment, Tait Electronics Limited reserves the right to update the equipment or this document or both without prior notice. Intellectual Property Rights This product may be protected by one or more patents or designs of Tait Electronics Limited together with their international equivalents, pending patent or design applications, and registered trade marks: NZ409837, NZ409838, NZ508806, NZ508807, NZ509242, NZ509640, NZ509959, NZ510496, NZ511155, NZ511421, NZ516280/NZ519742, NZ520650/ NZ537902, NZ521450, NZ522236, NZ524369, NZ524378, NZ524509, NZ524537, NZ524630, NZ530819, NZ534475, NZ534692, NZ535471, NZ537434, NZ546295, NZ547713, NZ569985, AU , AU , AU , AU , AU , CA , CA , CN , EU1,532,866, EU1,599,792, EU , EU , GB , GB , GB , GB , US11/232716, US10/597339, US10/520827, US5,745,840, US10/547653, US10/546696, US10/ 546,697, US10/520827, US10/547964, US10/ , US11/572700, US29/ This product may also be made under license under one or more of the following U.S. Patents: 4,590,473 4,636,791 4,716,407 4,972,460 5,146,497 5,148,482 5,164,986 5,185,795 5,185,796 5,271,017 5,377,229 5,502,767. The IMBE voice coding Technology embodied in this product is protected by intellectual property rights including patent rights, copyrights and trade secrets of Digital Voice Systems, Inc. This voice coding Technology is licensed solely for use within this Communications Equipment. The user of this Technology is explicitly prohibited from attempting to decompile, reverse engineer, or disassemble the Object Code, or in any other way convert the Object Code into a human-readable form. Protected by U.S. Patents 5,870,405 5,826,222 5,754,974 5,701,390 5,715,365 5,649,050 5,630,011 5,581,656 5,517,511 5,491,772 5,247,579 5,226,084 and 5,195,166. Environmental Responsibilities Tait Electronics Limited is an environmentally responsible company which supports waste minimization, material recovery and restrictions in the use of hazardous materials. The European Union s Waste Electrical and Electronic Equipment (WEEE) Directive requires that this product be disposed of separately from the general waste stream when its service life is over. For more information about how to dispose of your unwanted Tait product, visit the Tait Electronics WEEE website at Please be environmentally responsible and dispose through the original supplier, or contact Tait Electronics Limited. Tait Electronics Limited also complies with the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS) Directive in the European Union. In China, we comply with the Measures for Administration of the Pollution Control of Electronic Information Products. We will comply with environmental requirements in other markets as they are introduced. 2 TaitNet P25 Conventional System Manual

3 Contents Preface Network Overview Example Installation Linking Infrastructure Routed Network Switched Networks Network Signal Paths Dual Mode Channel Groups Dispatch Console Support Analog Console Systems Digital Console Systems Encryption Network Management Uplink and Downlink Voting Simulcast Standard Conventional TaitNet P25 Network Other System Designs Simple Repeater Single Base Station Single Base Station with P25 Console Gateway Cross-Band Repeater Cross-Mode Repeater Legacy System with TB9100 Base Stations Added Making the Transition to Digital Channel Group Overview Types of Channel Group Single Base Station Single Transmitter with Fill-in Receivers Multiple Transmitters with SU Voting or Scanning Multiple Transmitters with Simulcast Channel Group Applications Channel Group with Digital Dispatcher Channel Group with Analog Dispatcher Channel Group Operation Selecting a Voice Stream Selection Criteria Voting TaitNet P25 Conventional System Manual 3

4 Centralized Voting Distributed Voting Switched Voting Voting Criteria Transmit Timing Function of the Transmit Buffer Transmit Timing in Distributed Voting Transmit Timing in Central Voting Transmit Timing in Simulcast Dispatcher Control of Channel Group Channel Control Commands Channel Control Messaging Simulcast Self-calibration Tait Simulcast Modulation Channel Group Configuration Network Access Codes Single User Group Community Repeater Hybrid Operation Special Receive NAC Values RF Repeat Simplex/Duplex Simulcast Voter Type Centralized Voting Distributed Voting Transmit Timing Distributed Voting Centralized Voting Centralized Voting (with Synchronization) Collective Channel Control Enabling Collective Channel Control Setting Up Wildcard Channel Control Commands Using Task Manager Digital Fixed Station Interface Channel Control Unsupported DFSI Commands Analog Line Interface Channel Control Subscriber Signaling Function Tone Subscriber Signaling Network Design Network Elements TB9100 Base Station P25 Console Gateway TaitNet P25 Conventional System Manual

5 5.2 Topology Channel Group Design Factors Number of Members Preamble Length Marshalling Duration Central Voter Arrival Time Skew Simulcast Providing a 1PPS Signal Minimizing the Delay Spread Problem Differential Doppler Effects Linking Capacity Variables Linking Options Determining the Number of Voice Streams Estimating the Link Capacity Requirement Example Calculations Task Manager Scripting Scripting Tips Example 1: Joining and Splitting Channel Groups Example 2: Fallback Mode Example 3: Backup Channels RF Linking Uses and Limitations Determining Site Suitability Configuration Overview Call Handling Understanding and Optimizing RF Linking Using a Repeater as One End of the Link Channel Groups with Multiple RF Links Security Options CSS Access Codes Base Station Passwords Policy Options Firewall Remote Access and Support from Tait VPN Access Dial-Up Access Making the Transition to Digital Using Spare Channels Using Zones Other Tips Example Plan Example Plan Network Management Using the Customer Service Software Monitoring Channel Group Voting Example Voter Monitoring Displays TaitNet P25 Conventional System Manual 5

6 Monitoring Quality of Service Using a Syslog Collector Call Records Alarms Archiving Log Files Example Messages Notifying Base Station Failure Talkgroup and Individual IDs Monitoring and Troubleshooting Simulcast Channel Groups Expected System Performance Routine Maintenance Relevant Base Station Alarms Monitoring Channel Group Status Monitoring Synchronization Monitoring Network Jitter Monitoring the RF Interface Checking Coverage in the Field Finding the Cause of High BER Appendix A Layered Protocols Appendix B Syslog Message Format PRI HEADER MSG TaitNet P25 Glossary Index TaitNet P25 Conventional System Manual

7 Preface Scope of Manual This manual describes the TaitNet P25 conventional network. It provides an overview of the network, describes the channel group and how it operates, discusses aspects of the network design, and gives practical assistance on how to manage an existing network. Document Conventions File > Open means click File on the menu bar, then click Open on the list of commands that pops up. Monitor > Module Details > Channel Module means click the Monitor icon on the toolbar, then in the navigation pane find the Module Details group, and select Channel Module from it. Within this manual, four types of alerts are given to the reader: Warning, Caution, Important and Note. The following paragraphs illustrate each type of alert and its associated symbol. Warning!! This alert is used when there is a potential risk of death or serious injury. Caution This alert is used when there is a risk of minor or moderate injury to people. Important This alert is used to warn about the risk of equipment damage or malfunction. Note This alert is used to highlight information that is required to ensure procedures are performed correctly. TaitNet P25 Conventional System Manual 7

8 Associated Documentation The full customer documentation set for TaitNet P25 networks is provided on the product CD supplied with TB9100 base stations. Updates may also be published on the Tait support website. Technical notes are published from time to time to describe applications for Tait products, to provide technical details not included in manuals, and to offer solutions for any problems that arise. Publication Record Issue Publication Date Description 1 February 2007 First release 2 November 2007 Release for TaitNet P25 networks with Version 3.12 base stations and P25 GC console gateways. Simulcast (synchronized) operation and configuration. Monitor command. Transmit timing. Task Manager scripting. Channel group design factors. Network design for simulcast. Monitoring quality of service. 3 March 2008 Release for TaitNet P25 networks with Version 3.20 base stations and P25 console gateways. Effect of differential Doppler. Security options (base station passwords, CSS access codes). Small changes to the description of voting operation. Initial buffer parameter renamed to Preamble. 4 April 2008 Channel group with multiple RF links (allow loopback). Scope is now conventional networks only. 5 January 2009 Release for TaitNet P25 networks with Version 3.30 base stations and P25 console gateways. Monitoring and Troubleshooting Simulcast Channel Groups. Encryption section expanded. Information about Tait Simulcast Modulation modified. Cancel P25 Unit call option added. 8 TaitNet P25 Conventional System Manual

9 1 Network Overview A TaitNet P25 network is a set of interconnected TB9100 base station transceivers. Each TB9100 can receive from and transmit to mobile and portable radios, just like any base station/repeater. However, TB9100s also have built-in networking capabilities that enable them to combine together to form one or more logical channels with wide area coverage. When a P25-capable 2-way radio (referred to as a subscriber unit or SU) makes a call, a TB9100 receives it and passes it over the linking infrastructure to other TB9100s, which can repeat the transmission. Third-party dispatch console systems can be integrated with TaitNet P25 networks. Often, they connect via a Tait P25 console gateway. P25 console gateways have the same networking capabilities as TB9100 base stations, but they have no RF capability. They can serve as an encryption/decryption point to enable analog dispatch consoles to participate in encrypted calls. TB9100 base stations and P25 console gateways are the main network elements in a TaitNet P25 network. They have voting capabilities and an Ethernet interface, so that extra modules such as voting comparators and digital interfacing equipment are not required. They are interconnected over an IP-based linking infrastructure. TB9100 IP/ Ethernet IP/ Ethernet TB9100 TB9100 P25 Console Gateway IP/ Ethernet IP/ Ethernet Linking Infrastructure IP/ Ethernet IP/ Ethernet Customer service software Time Syslog collector Console system The TaitNet P25 network is managed using the Customer Service Software (CSS) and a syslog collector. The CSS can connect to any Tait network element from anywhere in the network or beyond. It can remotely monitor and configure the connected network element. It can also carry out TaitNet P25 Conventional System Manual Network Overview 9

10 diagnostic tests and upgrade firmware. A third-party syslog collector acts an an alarm center, receiving alarms and call records from any network element, displaying them, and storing them in logs. The linking infrastructure passes voice over IP and signaling messages between network elements. It also carries CSS and syslog communications. TaitNet P25 networks comply with the APCO P25 set of standards. This means, for example, that they support dual mode (digital P25 and analog FM) operation and the use of P25-compliant mobiles and portables from other manufacturers. 1.1 Example Installation In the following simple example of an installed TaitNet P25 network, analog dispatch equipment is connected via the base station s analog line. Two channels are located remotely at different sites, resulting in a star topology. This means that there are never more than two hops from one base station to another. As all three channels operate as one, conversations are automatically transmitted from all the base stations. The TaitNet P25 network is linked via a firewall to the police LAN. The maintenance technician s PC running CSS and another PC serving as a syslog collector are part of that LAN. T B TB Site facility 1 0 TB Police Branch T B 8 T B TB9100 Telephone Exchange Router Hub Firewall Syslog CSS collector Ti m e P25 Console Gateway Console system Key RF cable Telco line Ethernet Analog line Police HQ 10 Network Overview TaitNet P25 Conventional System Manual

11 1.2 Linking Infrastructure The linking infrastructure is what interconnects the TB9100 base stations to form a TaitNet P25 network. It is IP-based and consists of LAN equipment at each site and a bearer network of links that interconnect the sites. The LAN equipment belongs to the TaitNet P25 network, while the bearer network can be leased from a telephone company. The linking infrastructure uses the same type of equipment as the public internet. However, the public internet itself is unsuitable for providing the linking infrastructure because it doesn t guarantee the necessary performance and security. The linking infrastructure can be integrated with an organization s LAN. This makes it possible for PCs running CSS or a syslog collector to connect from anywhere in the organization via the existing LAN. However, access control or a firewall should be provided for security and to restrict the traffic on the bearer network to TaitNet voice, CSS, and (in the future) subscriber unit data. There are two main types of linking infrastructure. Routed networks are WANs that connect sites using routers. They are suited to low-bandwidth links. Switched networks are LANs. They have a lower delay but require high-bandwidth links. Switched networks only use routers for linking the TaitNet P25 network with the organization s LAN. Routed Network In routed networks, each site has its own LAN segment. Routers are the interface between the LAN segments and the bearer network. They convert the data between Ethernet and other protocols such as T1 (for feeding to the bearer network) and vice versa. TaitNet P25 Conventional System Manual Network Overview 11

12 TB9100 TB9100 TB9100 CSS TB9100 Switch Switch TB9100 Router Router TB9100 TB9100 Site 2 Site 3 TB9100 TB9100 Switch TB9100 TB9100 Switch Router Master router with firewall Syslog collector Organization's LAN TB9100 Site 1 CSS This example uses a star topology, which limits the number of router hops to two even with a larger number of sites. Only Tait-approved routers can be used and they must be configured for particular requirements such as IP multicast and Quality of Service (to give the voice stream priority over other data). The bandwidth requirements can be reduced by the use of compressed RTP. Switched Networks In switched networks, switches are used instead of routers to link sites. The whole TaitNet P25 network is essentially a single LAN. This is achievable if the remote links between sites have a sufficient bandwidth. The TaitNet P25 network can be integrated with the organization s LAN by configuring each as a separate VLAN (virtual LAN). Then a router is needed to route data between VLANs, in this case to enable the CSS and the syslog collector to operate from within the organization s LAN. 12 Network Overview TaitNet P25 Conventional System Manual

13 TB9100 TB9100 TB9100 CSS TB9100 TB9100 Switch Bearer Network Switch TB9100 TB9100 Site 2 Site 3 TB9100 TB9100 TB9100 Syslog collector TB9100 Switch Router with Firewall Organization's LAN TB9100 Site 1 Key CSS VLAN 1 VLAN 2 The links between switches need to have sufficient bandwidth to ensure minimal jitter. Switches are not normally able to prioritize voice over IP packets. 1.3 Network Signal Paths The base stations receive calls from SUs. In digital P25 mode, these communications are in the IMBE format, with forward error correction added. The base stations correct any errors and remove the forward error correction bits. They put the result on the network as voice over IP using RTP (the Internet real-time protocol). Routers or switches pass the RTP packets to the router, and then over the bearer network to other network elements. P25 console gateways convert these communications to suitable protocols and pass them to the dispatch console equipment. If this equipment is digital, the DFSI protocol is used. If the equipment is analog, voice is converted to analog and any subscriber signaling can be converted into its MDC1200 equivalent. TaitNet P25 Conventional System Manual Network Overview 13

14 Analog FM calls can also be networked. The received voice is put into the G.711 digital format and sent out using RTP. G.711 needs more bandwidth than IMBE. TB9100 IMBE voice + signaling/ Common air interface IMBE VoIP/ Ethernet TB9100 P25 Console Gateway Analog audio + signaling IMBE VoIP/ Ethernet IMBE VoIP/ Ethernet Linking infrastructure Syslog messages/ IP/Ethernet Data/IP/ Ethernet CSS Time Analog console system Syslog collector In addition to this voice traffic, the linking infrastructure carries alarm messages and CSS communications. Alarms and other status indications can be sent to a syslog collector. A PC running the CSS can communicate with any base station on the network, monitoring it, changing its configuration, or carrying out diagnostic tests. 1.4 Dual Mode The TaitNet P25 network supports dual-mode operation. TB9100s can receive and transmit in digital P25 and in analog FM mode and the network can carry speech for both modes. If a TB9100 receiver s RF interface is configured for dual mode, it listens for digital P25 signals. If it detects them, it switches to digital P25 mode, otherwise it receives in analog FM mode. When a dispatcher initiates a call, the TB9100 transmits in the default mode for the channel, unless the console selects a different calling profile. 14 Network Overview TaitNet P25 Conventional System Manual

15 Base stations operating in dual mode operate to their full specification, even if the analog FM mode is wide-band. An additional filter in the digital front end means that the receiver can listen for analog FM with a wide-band setting and for digital P25 using a narrow-band filter. Sensitivity and selectivity for digital P25 signals are largely unaffected by dual-mode operation. 1.5 Channel Groups TaitNet P25 networks consist of one or more channel groups. Each channel group is a single logical channel that provides a distributed RF receive and transmit function. Typically, a channel group contains one base station from each site in the TaitNet P25 network. This means that the channel group coverage extends over the entire network area. Channel groups can interface to digital dispatch equipment, to analog dispatch equipment, and to a trunking site controller. The dispatch equipment often interfaces via a P25 console gateway. A base station can only be a member of one channel group at a time. Channel groups are implemented using IP multicast. To assign a base station to a channel group, you configure it with the channel group s multicast address. When an inbound RF signal arrives at a base station, it is sent to the multicast address. All channel group members are listening to that address; they receive the signal from the network. If their repeat function is enabled, they broadcast the signal. If more than one signal arrives at once, a voting and switching process determines which signal the channel group transmits. This is carried out by the channel group itself. No external equipment is required. 1.6 Dispatch Console Support Dispatchers communicate over a radio channel with SUs. TaitNet P25 networks facilitate this communication. Dispatch equipment can be lineconnected to a single TB9100 base station or to a whole channel group. If there are multiple dispatcher positions, the dispatch equipment usually has some kind of console switch to enable the dispatcher to select the channel to talk on. Often, dispatch equipment is connected to the TaitNet P25 network via a P25 console gateway. The P25 console gateway provides an analog line if the dispatch equipment is analog or a DFSI interface if the equipment is digital. Alternatively, dispatch equipment can be connected directly to a base station in the channel group. With the appropriate feature licenses, any TB9100 can provide an analog line interface or a DFSI interface. TaitNet P25 Conventional System Manual Network Overview 15

16 Analog Console Systems The TaitNet P25 network supports line signaling, tone remote function tones and Motorola MDC1200 signaling. During analog FM calls, the network is transparent to analog signaling; analog voice and signaling is converted into the G.711 format for transport across the IP network. During digital P25 calls, any analog signaling from the console is mapped to the P25 standards for transport across the air interface. With the appropriate feature licenses, the P25 console gateway can function as an encryption/decryption point. Digital Console Systems Digital console systems connect to a channel or channel group using the DFSI interface defined in the P25 TIA standard. Encryption and decryption is carried out by the console system. The DFSI interface supports analog FM mode. 1.7 Encryption All TaitNet P25 networks support end-to-end encryption between radios. No additional network licenses or configuration settings are required. The network simply passes on the encrypted data or voice. If analog dispatch equipment needs to participate in encrypted calls, a P25 console gateway is needed to provide an encryption/decryption point. Tait SUs and P25 console gateways can be provided with keys using the handheld Tait Key Fill Device (KFD). This is able to create keys, load them into Tait SUs (and P25 console gateways), change keysets and zeroize unwanted keys. If the network has SUs from other manufacturers, a compatible key fill device is required. For example, Motorola SUs can be provided with keys using the Motorola KVL The KVL3000+ can also be used with of Tait SUs, but needs a Tait 9000 series to KVL3000+ adapter ( TPA-SV-020). See MTA xx for instructions on using the KVL3000+ for key management of Tait SUs. A Tait Key Management Facility is in development which will manage encryption keys and rekey radios over the air (OTAR); contact Tait for more information. 16 Network Overview TaitNet P25 Conventional System Manual

17 1.8 Network Management Using the Tait CSS software, you can remotely connect to any Tait network element and monitor or configure it. The CSS can monitor the current status of all alarms in the connected network element and display its call record log or system log, containing alarms and other messages. The CSS can also monitor voting in a channel group, conduct diagnostic tests, and upgrade firmware. The TaitNet P25 network can also be set up with a syslog collector. This can receive alarms and call records from any network element, displaying them and logging them to file. It can also monitor heartbeat messages. In this way, you can monitor the whole network from a single location. 1.9 Uplink and Downlink Voting In conventional networks, uplink voting and downlink voting (and also simulcast, see Simulcast on page 18) are options that automate the handover from one base station to another. If a network doesn t have downlink voting or simulcast, SU users must manually change channel as they move from the coverage area of one base station to another. This cannot be done without terminating the call and starting another. With uplink voting, the base stations in a channel group are all on the same receive frequency. The channel group compares all the signals received and provides the best signal to the dispatcher and (if RF repeat is enabled) to the channel group transmitters. With downlink voting, the SUs rapidly sample the signals from the channel group transmitters and select the best signal. The base station transmitters are configured to transmit a preamble before the call itself, and to begin transmitting at approximately the same time (otherwise SU voting would compare different signals and give misleading results). The SUs are configured to continuously scan their list of channels looking for activity. When activity is detected, the RSSI of all channels on the list is measured, and then the SU switches to receive the one with the best RSSI. Uplink and downlink voting combine to completely automate the process of channel selection. Dispatchers and SU users can listen and speak without needing to first switch to the correct channel. Downlink voting does add to the voice delay of the system. The more channels to be voted on, the greater the delay. Refinements in SU voting procedures can mitigate the increase in voice delay but not remove it. To eliminate manual channel switching without adding to the downlink voice delay, simulcast is required. TaitNet P25 Conventional System Manual Network Overview 17

18 1.10 Simulcast Simulcast is the simultaneous broadcast of the same signal from several base stations, all of which transmit on exactly the same frequency. Simulcast is nearly always combined with uplink voting. Simulcast brings the following benefits to conventional operation: Economical in use of frequencies. The transmitters in a simulcast area all use the same frequency. Seamless roving. Users do not need to manually switch channels as they move out of the coverage area of one base station and into another. The SU always receives and transmits on the same frequency. Uplink voting handles the handover from one coverage area to another. All-informed coverage over a very wide area. Simulcast systems can improve signal quality because the combined signal from several transmitters is stronger. However, there can also be a degradation in signal quality in some parts of the area of overlapping coverage, but this is minimized by the use of a modulation scheme designed for simulcast (such as Motorola s LSM or Tait s TSM), by tight control of the carrier frequency and the deviation accuracy, and by careful site planning and system design (see Simulcast on page 67). Simulcast requires exact timing of transmissions. This timing is provided to each transmitter by a 1PPS pulse from a GPS-disciplined timing reference. TaitNet P25 networks (both conventional and trunked) can be simulcast. All simulcast transmitters on one channel belong to the same channel group, which provides uplink voting. Voting must be centralized so that the central voter can synchronize transmissions exactly. The simulcast in TaitNet P25 networks is digital, which means that analog FM calls cannot be synchronized and that simulcast systems are not dual-mode Standard Conventional TaitNet P25 Network A conventional TaitNet P25 network often consists of several sites and many channels, allowing several channel groups to co-exist in the one network and supporting several dispatcher positions. In the example below, there are three channel groups, each having one TB9100 at each of three sites. As the linking infrastructure consists of third-party equipment that forms the building blocks of the Internet, it can easily be scaled up as needed. Each channel group can be connected via a P25 console gateway to an analog console. Alternatively, any channel group member can have a DFSI interface to a digital dispatch console. The channel group design supports the connection of additional consoles, to provide redundancy. 18 Network Overview TaitNet P25 Conventional System Manual

19 TB9100 TB9100 TB9100 TB9100 TB9100 TB9100 TB9100 TB9100 TB9100 Bearer Network CSS TB9100 P25 TB9100 Console Gateway Console switch Syslog collector Time Time Time Dispatcher positions If the base stations in a channel group have the repeat function enabled, that channel group acts as a wide-area repeater (however, dispatcher calls have priority over radio calls for transmitting over the air). If the repeat function is disabled, the channel group acts as a wide-area lineconnected base station. Calls received by any base station are sent to the dispatcher and calls from the dispatcher are transmitted via all the base stations. TaitNet P25 Conventional System Manual Network Overview 19

20 1.12 Other System Designs TB9100 base stations and P25 console gateways can be part of systems other than a standard TaitNet P25 network. The following examples show some of the options, beginning with the simplest. Simple Repeater A single TB9100 can be configured to operate as a simple P25-compliant repeater. Its Ethernet interface is only used for communications with the CSS. The CSS can be connected using either an ordinary or a cross-over Ethernet cable. TB9100 IP/ Ethernet CSS If remote access is required, the installation needs a router and a switch. Single Base Station A TB9100 can be configured to operate as a simple P25-compliant base station, connected to a third-party dispatch console. If the console is analog, it connects to the TB9100 via the analog line. If the console is digital, it connects via DFSI over IP. TB9100 Time With an antenna relay, the base station can operate in simplex mode. This only requires a single antenna and one operating frequency for both transmitting and receiving. The repeat function must be disabled. 20 Network Overview TaitNet P25 Conventional System Manual

21 Single Base Station with P25 Console Gateway Third-party console equipment can be connected to the base station via a P25 console gateway. The console equipment is connected to the gateway via an analog line (analog equipment) or via the DFSI (digital equipment). The P25 console gateway communicates with the TB9100 using proprietary Tait channel group communications (the TB9100 and the P25 console gateway are effectively a channel group). TB9100 IP/ Ethernet Linking infrastructure IP/ Ethernet CSS IP/ Ethernet P25 Console Gateway DFSI or analog line Time Dispatch console Cross-Band Repeater The TB9100 s built-in channel group interface makes creating a cross-band repeater straightforward. Two base stations (for example one UHF and the other VHF) are joined via a switch and are configured to belong to the same channel group. They can operate in both analog FM and digital P25 modes, but do not provide a cross-mode capability (analog FM to digital P25 or vice versa). This topology can easily be extended to provide cross-band repeating between three frequency bands. TB9100 (UHF) IP/ Ethernet Switch IP/ Ethernet CSS TB9100 (VHF) IP/ Ethernet TaitNet P25 Conventional System Manual Network Overview 21

22 Cross-Mode Repeater In a cross-mode repeater, one TB9100 operates in digital P25 mode and another TB9100 (or legacy base station) operates in analog FM mode. The base stations must be connected by analog line. This is because channel groups do not support converting a call between analog FM and digital P25 modes. E & M signaling is required to key the transmitters. TB9100 base stations can be connected by their analog lines for other purposes as well. This may be cost-effective if there is no existing IP-based infrastructure, but voice quality is reduced and signaling information is lost. Legacy System with TB9100 Base Stations Added TB9100 base stations can be added to existing systems. The existing bearer network can be used. The bearer circuits connect the console system to the TB9100s via their analog interfaces. In this topology, there is no IP-based network, although one could be set up to provide remote CSS access to the TB9100s. The TB9100s can operate in analog FM or digital P25 mode. Analog base station Time Dispatcher position Analog base station TB9100 Legacy circuit-switched bearer network (leased lines) Console switch Time Dispatcher position Time Dispatcher position TB9100 Time IP/ Ethernet CSS Dispatcher position 22 Network Overview TaitNet P25 Conventional System Manual

23 1.13 Making the Transition to Digital The dual-mode capability of Tait TB9100 base stations gives network providers flexibility when making the transition from an existing analog conventional system to a new digital P25 network. TB9100s can replace analog base stations and interoperate with analog FM radios. Here are some possibilities: Add P25 radios and/or TB9100 base stations to the existing system. Operate initially in analog FM mode, but change later to digital P25 mode. Add digital P25 channels to the existing analog system. This lets the network provider begin with P25 while continuing the existing conventional capability. Set up a TaitNet P25 network, but configure at least some of the TB9100s to operate in analog FM mode, for the support of legacy analog radios. Purchase P25 radios as new or replacement radios are needed. When a talk group has all P25 radios, it switches to digital P25 mode for normal operation but can always change channel to interoperate with analog-only radios. When all groups use digital P25, change the base stations to operate only in digital P25. For more details, see Making the Transition to Digital on page 98. TaitNet P25 Conventional System Manual Network Overview 23

24 2 Channel Group Overview TB9100 base stations are designed to work together as channel groups. A channel group is a single logical channel that provides a distributed RF receive and transmit function. Often, a channel group has one member at each site in the network, so that it can provide coverage over the full network coverage area. Interface to/from channel group Channel group master Base station Base station Base station Channel group communications Site 1 Site 2 Site 3 The members of a channel group communicate with each other using an IP-based proprietary Tait protocol. If desired, the channel group can have a voting function enabled by software. This voting provides the best available RF signal for repeating and providing to external interfaces. A channel group member can provide a gateway function, offering an analog line interface, a trunking (TCCP) or a digital dispatcher (DFSI) interface to an external device. This member is referred to as the channel group master, as it exerts control over the channel group, based on commands it receives from the external device. P25 console gateways can be members of the channel group just like TB9100 base stations. A channel group can have up to 14 members. 24 Channel Group Overview TaitNet P25 Conventional System Manual

25 2.1 Types of Channel Group Channel groups of different types can be used in conventional and in trunked networks. Single Base Station You can regard a single base station as a channel group with one member. These base stations can be standalone repeaters or can have any of the gateway functions described above. A single base station s channel definitions still reference a channel group. The default configuration has a channel group for single base stations (LocalRepeater) that disables most channel group functions but still allows you to specify the preamble (transmit buffer level) to reflect the jitter of signals arriving on the interface. Optional interface Tx/Rx Single Transmitter with Fill-in Receivers A channel group makes it easy to extend the coverage of a base station by adding a number of strategically placed fill-in receivers. The transmitting base station is usually but not necessarily the channel group master. Continuous voting selects the best available RF voice stream for repeating and for providing to the dispatcher. Tx/Rx Rx Rx Multiple Transmitters with SU Voting or Scanning The channel group can have multiple transmitters. In conventional systems, SUs can be configured to scan the frequencies of the channel group transmitters and select the best downlink signal. Channel group receiver voting continually selects the best uplink signal for providing to the dispatcher and to other base stations for repeating. TaitNet P25 Conventional System Manual Channel Group Overview 25

26 Tx/Rx Tx/Rx Tx/Rx Multiple Transmitters with Simulcast In a simulcast network, the channel group transmitters all use the same downlink frequency. This is a useful option where channel frequencies are scarce or expensive. SUs do not need to scan, reducing the call setup time. Simulcast makes sure that the transmissions are on exactly the same frequency and precisely synchronized. The base stations are also configured to use the same receive frequency. Continuous channel group voting selects the best uplink signal for providing to the dispatcher and to other base stations for repeating. 2.2 Channel Group Applications Digital or analog dispatch equipment can be connected to a channel group. From the dispatch equipment s perspective, the channel group is just like a single channel, except for the wide-area coverage. Analog dispatch equipment connects via a P25 console gateway. A channel group can also function as a traffic channel or a control channel in a trunked network. Channel Group with Digital Dispatcher Digital dispatch equipment is connected to the channel group master. This can be a base station or a P25 console gateway. The master interfaces between the digital dispatch equipment and the channel group. Fixed station host DFSI Master Base station Base station Base station Voice transport Channel control Subscriber signaling Communication is via the P25 digital fixed station interface (DFSI). The dispatch equipment is known as the fixed station host (FSH). All communications between the channel group and the FSH pass through 26 Channel Group Overview TaitNet P25 Conventional System Manual

27 the master. The master and the FSH communicate using the DFSI protocol defined by the P25 standard. The master also communicates with the other members of the channel group. (IP allows the use of distinct protocols on the same physical interface.)the DFSI provides voice transport, channel control, and subscriber signaling services. Channel Group with Analog Dispatcher Analog dispatch equipment can also be connected to a channel group. The attachment is via a P25 console gateway or via the analog line of a base station. This converts between analog and digital P25 voice and signaling. The P25 console gateway can also serve as the encryption/decryption point for dispatcher communications. Analog dispatch equipment 4-wire E & M P25 Console Gateway Base station Base station The connection between the analog dispatch equipment and the P25 console gateway is the analog equivalent of the DFSI. Subscriber signaling (optional) is MDC1200 (also known as Stat- Alert ) Voice transport is 600 Ω 4-wire Channel control is tone remote and/or E & M line signaling TaitNet P25 Conventional System Manual Channel Group Overview 27

28 3 Channel Group Operation How do the members of a channel group work together as a single logical channel? When a signal appears at an interface, the member turns it into a voice stream. Voice streams are turned into RTP packets for sending to other members of the channel group. They are sent to a special type of IP address, a multicast address. All members of the channel group listen to the same multicast address. All of them are able to receive the RTP packets on their digital line and to transmit the digital voice signals contained in them. Dispatcher call handling For example, when a dispatcher initiates a call, the P25 console gateway turns the call into a voice stream and puts it as RTP packets on the TaitNet P25 network. The other members of the channel group receive the packets and transmit the call over the air. Base station Base station Base station P25 Console Gateway Time Console system 28 Channel Group Operation TaitNet P25 Conventional System Manual

29 SU call handling Similarly, if an SU transmits, a base station receives the signal, turns it into a voice stream and sends it as RTP packets to the channel group s multicast address. The P25 console gateway receives those packets and turns them into analog voice, which it sends to the analog dispatch equipment. If the base stations in the channel group have RF repeat enabled, they re-transmit the call. Base station Base station Base station P25 Console Gateway Time Console system Handling call contention If multiple signals come from different interfaces or different callers at the same time, a selection process chooses the voice stream with the highest priority (see Selecting a Voice Stream below). If multiple signals appear at the RF interface from the one caller, voting continually selects the voice stream with the best quality (see Voting on page 30). Each channel group member has a switch for making selecting and voting decisions. 3.1 Selecting a Voice Stream If the channel group receives more than one call at once, a selection process chooses one of the calls. These calls can arrive at different interfaces. Each channel group member selects the voice stream with the highest priority. The selection process is quite complex. Voice streams are classified into different types, depending on whether they originate from a dispatcher (usually an analog line or DFSI), an SU user (usually an RF interface), or the maintainer (usually a control panel microphone). Each outgoing interface applies its own rules. This means that dispatchers will get to hear a calling SU in preference to another dispatcher, but SU users will hear the dispatcher TaitNet P25 Conventional System Manual Channel Group Operation 29

30 in preference to another SU user. Calls higher on the priority table can also pre-empt existing calls. For example, if a call from an SU user is being repeated, and a dispatcher call is started, the channel group will transmit the dispatcher call. Selection Criteria If voice streams have the same priority, P25 calls are selected in preference to analog FM calls. If the calls are the same type, the voice stream from the channel group member with the lowest receiver number is selected. If there are no receiver numbers, IP addresses are used instead. 3.2 Voting The channel group itself is able to continually vote at packet level on the voice streams it receives from its RF interfaces. This enables it to repeat the best possible received signal and to provide that signal to the channel group s interfaces. In effect, voting blends or combines multiple voice streams, always picking the best packet out of those on offer. Voting is carried out by the same switches that handle the selection process described above. Voting can be centralized at one channel group member or distributed among all members. If the channel group receivers use different frequencies, there is no voting; the receivers are configured with the voting type switched. Using the DFSI, digital dispatch equipment can override the channel group s normal voting operation. It can select the voice stream from any channel group member or disable any member so that it does not participate in voting. Centralized Voting In centralized voting, one channel group member carries out the voting. All voice streams are sent to that member. P25 voice streams originating at an RF interface are voted on every voice codeword (20ms), resulting in a high quality voice stream. Analog FM voice streams are voted 5 times per second. Voice streams that didn t originate at an RF interface also pass through the central voter s switch. A skew (differences in the arrival time of different streams from the same caller) of up to 100ms can be compensated for in digital P25 mode but not in analog FM. The central voter must have a transmitter: fill-in receivers and P25 console gateways cannot be central voters or backup central voters. To avoid having a single point of failure, a second channel group member can be configured for central voting. It will take over as the central voter if 30 Channel Group Operation TaitNet P25 Conventional System Manual

31 the first member fails (this can take up to 30 seconds). When more than one member is configured as a central voter, the member with the lower receiver number becomes the central voter. The other member operates as a satellite voter. Centralized voting is required for simulcast networks. It is the best option for star topologies. It gives optimal results if the longest network delay from a member to the central voter is <40ms and reasonable results if the longest delay is <80ms. Distributed Voting When voting is distributed, all the base stations in the channel group that are receiving valid RF signals vote in concert. If a base station wins the vote, it sends its voice steam to the channel group. If it loses the vote, it ceases sending its voice stream to the channel group, to save linking bandwidth. Voting occurs every LDU (180 ms). Distributed voting may work better for non-star topologies or where receiver coverage does not overlap. It gives optimal results if the longest network delay from one member to another is <40ms and reasonable results if the longest delay is <80ms. Switched Voting The switched voting type is selected when channel group receivers have different frequencies. It effectively disables RF voting. There is no blending of streams from different sources. Instead, if more than one call is received on the channel group s RF interfaces, the call from the base station with the lowest receiver number (or IP address) wins, even if it arrived later. A call cannot be outvoted by another signal of better quality. However, if the first call was analog FM and a subsequent call is digital P25, the subsequent call takes over, pre-empting (replacing) the analog FM call. Voting Criteria The following criteria determine the outcome of central or distributed voting: If the streams have the same type, the stream with the best signal quality wins the vote. Generally, the impairment is used. This is the inverse of signal quality and its value is included in voice streams. The impairment varies between 0 (best signal quality) and 15 (worst signal quality). The central voting of digital P25 streams uses the number of corrected errors instead of impairment. If the streams have the same impairment, the stream at the member with the lowest receiver number wins the vote. TaitNet P25 Conventional System Manual Channel Group Operation 31

32 3.3 Transmit Timing When there are multiple transmitters in a channel group, they need to begin transmitting a call together. Together may not mean at exactly the same time, but within an appropriate timing window. The size of this timing window varies with the system design. If the transmitters use different frequencies, transmit timing needs to ensure that one transmitter does not transmit so much later than the other that it interferes with natural conversation. Network designers should aim for a timing window of around 100ms. If the channel group has downlink voting, the transmit timing window needs to be small enough so that when SUs start scanning and voting, all members are transmitting. Network designers should aim for a timing window of a few milliseconds. If the channel group is simulcast, transmit timing needs to be exact, so that in areas of overlapping coverage, the signal arrives simultaneously from the transmitters involved. Members have a 1PPS timing pulse that enables timing with microsecond precision. The central voter automatically adjusts the marshalling duration to compensate for network delay and jitter. System installers can adjust the launch time in microsecond increments, to shift the area within which the signal arrives simultaneously. Transmit timing is adjusted by means of voter configuration parameters, see Transmit Timing on page 45. These parameters configure the preamble duration and compensate for network delay and jitter. Channel groups use different parameters, depending on whether they are synchronized or not. Function of the Transmit Buffer Each base station has a transmit buffer. This buffer plays an essential role in transmit timing. After the voice stream has begun arriving at a base station and before it s time to start transmitting the call, the transmit buffer stores the arriving packets, later providing them to the transmitter as needed. In this way, it is able to compensate for differences in network delay between members of the channel group so that they transmit together. The transmit buffer has two other functions: compensating for jitter and storing arriving packets while a call preamble is transmitted. In unsynchronized channel groups, the size of the transmit buffer at the beginning of the call is determined by the configured duration of the preamble. Jitter Jitter is the variation in packet arrival time. If packets arrive late, the transmit buffer provides stored packets to the transmitter. It empties until the packets arrive. The larger the jitter, the bigger the jitter buffer needs to be, and the greater the call delay, because more packets need to be stored in the buffer before the call can begin. If the jitter is so large that the buffer runs out of packets, a buffer underflow occurs. The transmitter fills the gap with packets 32 Channel Group Operation TaitNet P25 Conventional System Manual

33 that encode silence. If several silence packets are needed to fill a gap, users notice the glitch. Jitter has various sources. The network element providing the voice stream produces a jitter of about 10ms. This is the delay variation in clocking out packets onto the Ethernet interface. Switches and routers also contribute to jitter. If there are packets in a queue, the switch or router takes longer to pass a packet through. When a channel group has distributed voting, the handover from one member to another can result in a large delay, which is effectively another kind of jitter. Preamble In many networks, transmitters need to preface calls with a preamble. While the transmit buffer is filling, the transmitter transmits a preamble. If there is downlink voting, SUs can scan and vote during the preamble, acquiring a channel before the call begins. Even in networks without voting, a preamble can help SUs to more easily synchronize to the transmission. In unsynchronized channel groups, the duration of the preamble is determined by the Preamble parameter. In simulcast networks, a preamble is only required if there are multiple simulcast channels and SUs need to vote between them. If the marshalling time is self-regulating, the duration of the preamble is determined by the Buffer min setting. The regulation process ensures that the base station furthest from the central voter uses a preamble that is about the duration of the Buffer min setting. Other base stations receive the voice stream earlier, start transmitting preamble earlier, and therefore have a longer preamble. Transmit Timing in Distributed Voting Distributed voting is always unsynchronized. The voter configuration parameters used to adjust transmit timing in a channel group with distributed voting are the preamble and the hold-off time. The preamble is set to compensate for jitter or to provide a sufficiently long preamble. The hold-off time applies only when the member is repeating a call that it received on its RF interface. It tells the receiving member to wait for the voice stream time to traverse the network and arrive at the other channel group members, before beginning to transmit. Both timers begin when the signal arrives at the transmitter. (The preamble is also a timer, measured in milliseconds; if the preamble is 40ms, the transmit buffer has been filled by packets that take 40ms to arrive, when the preamble ends and the transmitter begins to transmit the call.) When a vote-winning call is received, the base station (A in the diagram below) sends it to the channel group. It waits for the hold-off time and then begins transmitting the call (assuming that this time is long enough to fill the buffer to the level specified by the preamble setting). The other members wait for the preamble duration before beginning to transmit the call, so that the buffer has an adequate level. While the buffer is filling, all members transmit preamble. TaitNet P25 Conventional System Manual Channel Group Operation 33

34 A B C Network delay to B Network delay to C Hold-off (A) Transmit Timing in Central Voting Central voting in non-simulcast channel groups is unsynchronized. A centrally voted channel group uses the same voter configuration parameters (hold-off time and preamble) as a channel group with distributed voting. However, only the central voter applies the hold-off time. It does this for all calls. (If the channel group is simulcast, transmit timing operates differently, see Transmit Timing in Simulcast below.) All received calls are sent to the central voter, which provides a voted output. The central voter s transmitter waits for its hold-off time and then begins transmitting (assuming that this time is long enough to fill the buffer to the level specified by the preamble setting). After beginning to receive the voice stream, the other members wait for the preamble duration before beginning to transmit the call. While the buffer is filling, all members transmit preamble. The preamble duration and the transmit buffer size at the start of the call is highest at the central voter and lowest at the member furthest from the central voter. If the central voter s hold-off time is the average network delay to the satellite voters, the channel group members begin transmitting the call as close as possible to one another. Transmit buffer level (at start of call) A Central voter C Network delay to A Hold-off Network delay to C Hold-off Transmit Timing in Simulcast Simulcast channel groups must have a central voter. They are synchronized, which means that transmit timing is under the control of the central voter. Configuration parameters (other than the local transmit offset) at other 34 Channel Group Operation TaitNet P25 Conventional System Manual

35 members have no effect. All voice streams pass through the central voter and are time-stamped. Members receive these time-stamped voice streams and transmit at the time indicated by the time-stamp. (They can delay transmission by a configurable local transmit offset of a few microseconds.) The time on the timestamp includes an allowance that gives the voice stream time to reach the furthest member and fill its transmit buffer to an adequate level. This allowance is referred to as the marshalling duration. Normally, the central voter regulates the marshalling duration based on feedback it receives from members. If the size of a member s transmit buffer falls below the configured Buffer min value, the central voter increases the marshalling duration. If the smallest transmit buffer is greater than this value, the central voter reduces the marshalling duration. In this way, the central voter automatically regulates the marshalling duration around the configured minimum buffer size. A Central voter Network delay to C Marshalling duration C Min buffer size Launch time Alternatively, the central voter can be configured with a fixed marshalling duration, overriding the automatic regulation. Under fault conditions, synchronization can be lost. If the transmitter is configured to transmit when unsynchronized, it does not apply any transmit timing but simply begins transmitting when it receives the voice stream. When synchronization is restored, the transmitter flushes its buffer and transmits based on the timestamp. This causes a glitch. 3.4 Dispatcher Control of Channel Group When a dispatch console is connected to a channel group, the dispatch commands to change channel, enable/disable RF repeat or enable/disable monitor need to be carried out by each member of that channel group. As they are only received by the P25 console gateway or by a base station with an analog line or DFSI, there needs to be a process that passes on these commands to the other channel group members. This enables the dispatcher to exert control over the channel as a whole. This process is carried out by the channel group coordinator. TaitNet P25 Conventional System Manual Channel Group Operation 35

36 Enable RF repeat Base station Base station Enable RF repeat Enable RF repeat Base station The channel control coordinator is a software process inside the channel module of each channel group member. The channel control coordinators work together to implement channel control commands and to ensure that the states of all members are consistent. If collective channel control is enabled, a channel control coordinator sends any commands it receives to other members. Collective channel control is generally enabled when network elements belong to a channel group. See Collective Channel Control on page 50. Using the CSS, you can monitor the coordinator of the connected network element. If the dispatch console is connected via an analog line, the connected network element needs a Task Manager task that interprets the function tone signaling. 550 Hz function tone IF Tone remote detected (550) THEN Enable RF repeat P25 Console Gateway Base station Enable RF repeat Enable RF repeat Base station Channel Control Commands The following table gives an overview of the commands for which collective channel control is available. Note that the functions that some commands invoke can also be obtained through configuration. Command Function Selectable through Configuration? Can be Actioned by Task Manager? Collective Control Select channel number No Yes Selectable Enable/Disable repeat Yes Yes Selectable Select/Disable receiver No No Always Monitor squelch Yes Yes Selectable 36 Channel Group Operation TaitNet P25 Conventional System Manual

37 Channel Control Messaging Channel control messaging is handled by the channel group coordinator in each channel group member. When a member with a DFSI or analog line receives a channel control command, the coordinator acknowledges the command and multicasts it to the channel group. The coordinator also resolves any contention (for example if there is more than one dispatcher connected to the channel group) and ensures that members maintain a consistent state. The coordinators can handle members entering or leaving the channel group because of power failure, channel change, or other uncontrolled activities. 3.5 Simulcast Transmitter operation in simulcast channel groups differs in the following ways. The exact moment when each transmitter begins to transmit a call is determined by the central voter and controlled to within ± 1.5 µs. The central voter uses a marshalling time that is dynamically adjusted (to maintain an appropriate level of the transmit buffer at the furthest base station) or fixed by configuration. For details, see Transmit Timing in Simulcast on page 34. Transmitters undergo an automatic self-calibration to optimize transmit deviation. Transmitters usually use a modulation scheme designed to provide better simulcast performance. Self-calibration TB9100 base stations that have simulcast enabled undergo an automatic regular self-calibration, which improves the deviation accuracy from ± 0.5dB to ± 0.2dB. The self-calibration may trigger the Tx not ready alarm when you start a base station or change its operating frequency. Otherwise, the self-calibration lasts only about 100ms and is carried out when the base station is not transmitting. Tait Simulcast Modulation As the simulcast performance of the C4FM modulation scheme is poor, Tait has developed the TSM modulation scheme. This is a constant envelope modulation, for use with non-linear transmitters. TSM improves the ability of SUs to cope with delay spread, at the cost of some selectivity and sensitivity as compared with C4FM. TaitNet P25 simulcast networks generally use TSM for the downlink, to take advantage of the improvements in delay spread capability. Tait P25 SUs TaitNet P25 Conventional System Manual Channel Group Operation 37

38 can all receive TSM. C4FM is used for the uplink (SU transmitting), but in repeater talkaround (direct mode), SUs must use channels configured for TSM transmission, because the SU receivers are configured for TSM. SUs that do not support TSM are not suitable for operation on simulcast networks with TSM downlinks. The Wide modulation scheme is also an option, where 25kHz channel spacing is available. 38 Channel Group Operation TaitNet P25 Conventional System Manual

39 4 Channel Group Configuration The operation of a channel group can be modified in various ways by changing configuration settings using the CSS. It is important that these settings are consistent across all members of the channel group. The following settings are relevant. 4.1 Network Access Codes Every P25 transmission contains a network access code (NAC). Transmitters must be configured with a transmit NAC. Receivers can be configured to only unmute to a particular NAC or to unmute to any NAC. The channel group responds to NACs in a similar way to an individual repeater. However, channel groups can also receive inputs from an analog line and/or a DFSI. If the channel group is transmitting signals originating from an analog line, it always uses the configured transmit NAC. If the signals originate from the DFSI and the channel group is configured to transmit the NAC from the voice stream, the channel group transmits using the NAC provided over the DFSI. The channel group also makes the received NAC available on the DFSI. NACs are configured in signaling profiles. You can enter a receive and a transmit NAC. The Accept any check box overrides the receive NAC and causes the receiver to unmute to any NAC. The From stream check box affects the transmitter and causes it to use the NAC in the voice stream in preference to the configured transmit NAC. Note Task Manager can configure base station behavior based on the NAC received. You can use this for particular applications, such as a selective cross-band repeater for VHF/800MHz. When the VHF receiver receives a particular NAC, it changes channel so that it belongs to a different channel group, which links it to the 800MHz repeater. You can configure a channel group for the following types of operation: Single User Group If the channel group is used by a single organization, SUs can transmit using one specific NAC. Base stations also transmit using another specific NAC. SUs only unmute to transmissions with the base station NAC and base stations only unmute to transmissions with the SU NAC. The NAC is not used for selective squelch (i.e. to identify a talkgroup). TaitNet P25 Conventional System Manual Channel Group Configuration 39

40 Normally, base stations are given the default NAC 0x293, unless there are other P25 base stations nearby that are using the same frequency. The Accept any and From stream check boxes are cleared Fixed station host DFSI Rx 114 Tx 293 Rx 114 Tx 293 Rx 114 Tx 293 Community Repeater If the channel group is used by different organizations, base stations can accept any NAC and re-transmit it. SUs transmit using the NAC for their organization. For this application, the Accept any and From stream check boxes should be selected. This tells the receiver to unmute to any NAC and also to transmit using the received NAC when the voice stream comes from the channel group (other base station) Fixed station host DFSI 293 Accept any Rx From stream 114 Tx Accept any Rx From stream 114 Tx Accept any Rx From stream 114 Tx Channel Group Configuration TaitNet P25 Conventional System Manual

41 If the digital dispatch console (FSH) provides a NAC, the From stream configuration ensures that the channel group uses that NAC when transmitting Fixed station host DFSI 55 Accept any Rx From stream 114 Tx Accept any Rx From stream 114 Tx Accept any Rx From stream 114 Tx 55 Hybrid Operation If base station transmitters from other organizations are causing interference, the channel group can be set up to transmit its own NAC but to receive any NAC. SUs are programmed to only unmute to the channel group NAC, so they ignore signals from transmitters belonging to other organizations Fixed station host DFSI 293 Accept any Rx 114 Tx Accept any Rx 114 Tx Accept any Rx 114 Tx 293 Special Receive NAC Values The APCO P25 standards specify two special receive NAC values. F7F lets a repeater receive any NAC and transmit the received NAC. F7E also lets a repeater receive any NAC but it transmits its own configured NAC. Tait has implemented these special values so that the receiver and the transmitter configuration are completely de-coupled. To configure a TB9100 for F7F operation, select the Accept any and the From stream check boxes. To configure a TB9100 for F7E operation, select the Accept any check box. TaitNet P25 Conventional System Manual Channel Group Configuration 41

42 4.2 RF Repeat If RF repeat is enabled in a standalone base station, the transmitter retransmits signals received on the RF interface. If RF repeat is enabled in the members of a channel group, the transmitters repeat the inbound RF signal. This could come from any receiver in the channel group. If voting is enabled, the channel group votes and provides the best signal for repeating and sending to other interfaces. If voting is disabled, the voice stream with the highest priority is selected. RF repeat is configured in the channel table. It can be enabled, disabled, or placed under dispatcher control. For digital dispatcher control of RF repeat, see RF repeat on page 53. For analog dispatcher control of RF repeat, see RF repeat on page 58. If RF repeat is dispatch-controlled, dispatcher commands can enable or disable it. If the dispatch equipment is connected to a channel group, members need to be configured to put RF repeat under collective control (see below). Then the dispatcher commands are passed on to all channel group members and do not only affect the connected member. An RF repeat command from the FSH directly turns RF repeat on or off. By contrast, analog dispatch equipment can only send particular tone remote function tones. These require Task Manager actions that turn RF repeat on or off in response to the function tones. 4.3 Simplex/Duplex The RF interface of a TB9100 base station is always duplex: it can transmit and receive at the same time. However, the channel group can be configured to be simplex or duplex. This refers to the IP links between channel group members. A simplex channel group can only handle one call at a time. It selects the one call with the highest priority. Dispatcher calls always win over subscriber calls. If the dispatcher is talking, he or she cannot hear an SU call. A duplex channel group can simultaneously handle an inbound (radio to dispatcher) and an outbound (dispatcher to radio) call. A dispatcher in a call can hear a subscriber call. Also, one dispatcher can hear another dispatcher and one SU user can talk and hear another SU user (provided voting is disabled and the SUs are duplex). You might expect that a simplex channel group only handles one voice stream at once, and that a duplex channel group handles two voice streams, one in each direction. In fact, voting and switching means that it is more complex than this. For example, a base station with an analog line can simultaneously send both an inbound and an outbound stream to the 42 Channel Group Configuration TaitNet P25 Conventional System Manual

43 channel group. For more details about the number of voice streams that the linking infrastructure needs to support, see Linking Capacity on page Simulcast For a channel group to operate in simulcast mode, its members must have the required feature licenses and be correctly configured. They must also have 1PPS and external reference frequency inputs. Reciters must have digital boards with hardware version or later (00.06 digital boards can be upgraded to 00.07, contact Tait for details). Note A simulcast channel group can have members that are not configured for simulcast. This can work in areas where their coverage area does not overlap with other members. To enable and configure a channel group member for simulcast 1. Provide the member with a Simulcast Transmitter feature license. (Not required for fill-in receivers.) 2. In the channel profile that the current channel will use, enable simulcast and choose appropriate settings. (See the CSS manual or Help for details.) a. In the General tab, select the modulation scheme that the transmitter will use. In the Status symbols list, select Channel, so that all transmitters send the same status. b. In the Synchronization tab, select the Simulcast check box. c. Choose appropriate settings for the other items in the Synchronization tab, based on the system design (see Simulcast on page 67). d. In particular, select or clear the Transmit if unsynchronized check box based on the network design. Aim to have a minimum reduction in coverage when synchronization is lost. You might select Yes if the area of overlapping coverage is small. Select No for one of the overlapping transmitters if the overlap area is critical. If all members are configured to stop transmitting when unsynchronized, loss of synchronization will result in no service at all. 3. In the channel group definition that the operating channel will use, Voting area, select the voting type. Select Central if the member will be the central voter or the backup central voter. For the other members, select Satellite. See Voter Type on page 44 for more details. 4. Configure the transmit timing appropriately for a simulcast channel group (see Centralized Voting (with Synchronization) on page 48). 5. Enable all simulcast alarms (Configure > Alarms > Control). They are disabled by default. TaitNet P25 Conventional System Manual Channel Group Configuration 43

44 6. Once all members of the channel group are configured, you can check the configuration and test the operation of the channel group. To monitor the simulcast status of an individual member, use the Simulcast monitoring form (Monitor > Synchronization > Simulcast). To monitor the simulcast operation of the channel group as a whole, use the Synchronized Transmit diagnostic test (Diagnose > RF Interface > Synchronized Transmit) and the Group Status form (Monitor > Channel Group > Status). 4.5 Voter Type The voting type (described above, see Voting on page 30) is selected in the Voting area of the Channel Group dialog box (select Configure > Channel Groups > Channel Group and click Edit.) This area also configures timers that enable channel group transmitters to transmit together (see Transmit Timing on page 45). Note Digital dispatch equipment can override the channel group s voting procedure and select a vote-winning receiver or disable any receiver. See Voter control on page 53. Centralized Voting Channel groups with star topologies are suited to centralized voting. Centralized voting is required for simulcast. To enable centralized voting 1. Choose two channel group members (one as the central voter and the other as the backup central voter). In a simulcast channel group, these members must be able to transmit. 2. Obtain central voter feature licenses for the two members. 3. Configure them with the voting type Central. Make sure that the backup central voter has a higher receiver number than the central voter. When the central voter is operating correctly, the backup central voter will operate as a satellite voter. 4. If desired, alter the maximum allowed skew. Voice streams that arrive at the central voter with a skew greater than the maximum allowed will be discarded. 5. Configure the other members with the voting type Satellite. These members must be version 3.05 or above for voting to be centralized. When the channel group begins operating, it starts voting in a distributed way. The central voter negotiates with the other members. Once it has 44 Channel Group Configuration TaitNet P25 Conventional System Manual

45 determined that there are no problems, it begins functioning as the central voter. The other members cease distributed voting and are now referred to as satellite voters. If the central voter fails, the other member configured as a central voter takes over. Distributed Voting To enable distributed voting, configure all channel group members with the voting type Distributed. 4.6 Transmit Timing Transmit timing is configured by the Voter area of the channel group configuration. The following sections explain how to do this for different voting types. Distributed Voting For each member of the channel group, configure transmit timing as follows. In the Channel Group profile that the current channel will use, select Distributed and enter hold-off and preamble values. (Members with distributed voting cannot currently be synchronized, so the settings in the Synchronized - network area do not apply.) The hold-off and preamble values compensate for network delay and jitter (or preamble). Hold-off In a channel group with distributed voting, hold-off is the length of time that the receiving base station waits before beginning to transmit the call. Set it to the average network delay from this member to the other members, if SUs scan and vote. Otherwise set it to 0 to reduce delay. TaitNet P25 Conventional System Manual Channel Group Configuration 45

46 A B C Network delay to B Network delay to C Hold-off (A) Preamble Set the preamble duration to the value required by SUs for voting or to the expected jitter (delay variation), whichever is the largest. The preamble duration determines how large the transmit buffer is at the start of the call and therefore how much jitter the transmitter can handle. SUs may, for example, need a preamble of 150ms in order to scan the channels and vote on the best signal before the call itself begins (avoiding late entry is particularly important with encrypted speech). In the case of a channel group with distributed voting, the jitter can be very large. If A is winning the vote, but suddenly loses the signal, it sends a fade message to the channel group. When B receives this message, it sends its received signal to the channel group. In this case, the jitter at A between the last packet provided by A and the first packet from B is twice the network delay between A and B. Signal to A fades A B C Fade message to B Voice stream B to C Jitter = 2 x network delay A -B 46 Channel Group Configuration TaitNet P25 Conventional System Manual

47 Centralized Voting For a centrally voted (but not simulcast) channel group, follow these steps to configure transmit timing. To configure the central voter 1. Enter a hold-off time equivalent to the average network delay needed for the voted stream to travel from the central voter to other members. 2. Set the preamble to the required preamble duration, if SUs require a preamble. SUs may, for example, need a preamble of 150ms in order to scan the channels and vote on the best signal before the call itself begins (avoiding late entry is particularly important with encrypted speech). If the SUs do not scan and vote, set the preamble to the expected jitter (delay variation), which is around 10ms for the path from the voter to the transmitter. The preamble value will only be used if it is larger than the hold-off time. Note Follow the same procedure for the backup central voter, but set a preamble based on the jitter for the path from the central voter to the backup central voter s transmitter. To configure satellite voters Connect to each of the remaining members in turn and configure them as follows. Set the preamble to the required preamble duration or to the expected jitter (delay variation), whichever is the largest. The jitter will be approximately 10ms plus the worst case network jitter for the network link from the central voter. Note Satellite voters do not use the Hold-off timer or any of the Synchronized - Network settings. TaitNet P25 Conventional System Manual Channel Group Configuration 47

48 Example In the following example channel group, the central voter s hold-off time is set to the average network delay, to minimize the variation in transmitter launch time between the three transmitters. The preamble duration is based on the jitter experienced by A and C. Preamble = 30 ms Hold-off = not used A Preamble = 30 ms Hold-off = 50 ms Central voter Preamble = 30 ms Hold-off = not used C Network delay = 60 ms Network delay = 40 ms Centralized Voting (with Synchronization) In a simulcast channel group, voting must be centralized and the central voter must be synchronized. The synchronized central voter determines the transmit timing of all simulcast members. At the central voter, configure the marshalling duration and a minimum buffer level for synchronized operation. You also need to configure members for unsynchronized operation, if they are configured to transmit when unsynchronized. This involves setting a preamble duration. The hold-off duration is not used (see Centralized Voting on page 47). To configure the central voter 1. In the channel group profile, select the voting type Central. 2. If desired, change the maximum skew. 3. Select the self-regulating marshalling option. 4. Enter a suitable value for the minimum buffer. This should be approximately the worst case network jitter for network links from the central voter to members plus an allowance of 20ms for jitter internal to the base stations. There is a trade-off between increasing the minimum buffer to handle high levels of jitter that occur rarely because of queuing at the router and the like, and decreasing the minimum buffer to minimize the call delay. (If a preamble is required, enter the preamble duration, if it is larger.) The central voter will adjust the marshalling duration around this value, see Transmit Timing in Simulcast on page Channel Group Configuration TaitNet P25 Conventional System Manual

49 Note Alternatively, you can override the self-regulating adjustment of the marshalling duration. Select the fixed marshalling option and enter a marshalling duration sufficient to maintain an adequate buffer level at the furthest member. This guarantees a fixed delay. 5. If the central voter is configured to transmit when unsynchronized, enter a value for the preamble duration. This defines the level of the transmit buffer before the central voter begins transmitting the call. The hold-off duration is not used. To configure the backup central voter 1. Configure the backup central voter in the same way as the central voter. 2. Give the backup central voter a higher receiver number than the central voter, otherwise it will routinely take over as central voter. To configure satellite voters There are no transmit timing requirements for satellite voters in a simulcast channel group that is synchronized, as the central voter determines transmit timing. If the satellite voter is configured to transmit when unsynchronized, enter a suitable value for the preamble duration. When the base station receives a late stream or is itself unsynchronized, it waits for the transmit buffer to fill to the configured level before beginning to transmit the call. Example In the following example simulcast channel group, the marshalling duration is automatically regulated around a minimum buffer level of 30ms. This will result in a marshalling duration of around 90ms. When the central voter timestamps the voice stream, it indicates a launch time that is the current time + marshalling duration. All transmitters begin transmitting at the launch time (however, each can be configured with a local transmit offset that delays the start by up to 200 microseconds). A and C report their buffer levels to the central voter. Having a greater network delay than A, C has the lower buffer level. The central voter will use that buffer level to adjust the marshalling duration. TaitNet P25 Conventional System Manual Channel Group Configuration 49

50 If the central voter is configured for a fixed marshalling duration, it needs to be given a value of 90ms. A Self-regulating: Min buffer size = 30 ms Fixed: Marshalling duration = 90 ms Central voter C Network delay = 40 ms Network delay = 60 ms Marshalling duration = 90 ms Launch time 4.7 Collective Channel Control Collective channel control is generally enabled in channel groups with a dispatch interface. It is enabled separately for channel change, enable/disable RF repeat, and monitor commands. Other commands (wildcard commands) can be propagated to the channel group using Task Manager. Enabling Collective Channel Control To enable collective channel control 1. In the channel group configuration of each member (Configure > Channel Group > Channel Groups and click Edit), set the channel control of the required dispatch commands to collective. 2. In the channel table of each channel group member, set RF repeat to DispatchControlled. 3. If the dispatcher interface is analog, set up Task Manager actions at the P25 console gateway that implement the dispatch command on receiving the relevant function tone. (It is necessary to implement the command at the Console Gateway even though this network element cannot repeat or monitor RF, so that collective control can pass the command on to the other channel group members.) Setting Up Wildcard Channel Control Commands Using Task Manager Channel control commands for which no collective control is available can be implemented by hand-coding the propagation to other channel group members. This is done using the Send function code Task Manager action. Please note that there is no monitoring of control status so that, if a member is out of service when the wildcard is propagated, it will be out of step with the rest of the channel group. 50 Channel Group Configuration TaitNet P25 Conventional System Manual

51 Important Do not use Task Manager tasks involving function codes for channel change, RF repeat, or Monitor commands. Put them under collective control instead. Figure 4.1 shows an example wildcard command. Figure 4.1 Propagating a dispatcher wildcard command IF Function code received (0) THEN Lock transmitter Base station Base station IF Function code received (0) THEN Lock transmitter Function code 0 Function code 0 Base station Function code 0 Linking Infrastructure Time Tone remote tone 550 P25 Console Gateway Function code 0 IF Tone remote detected (550) THEN Send Function code (0) Base station Console system To set up a wildcard command to disable selected transmitters 1. In the connected P25 console gateway, set up the Task Manager statement: IF Tone remote detected (550) THEN Send function code 0 Note You can select any function code between 0 and 255 as the equivalent of a tone remote function tone. 2. In particular base stations in the channel group, set up the following Task Manager statement: IF Function code received (0) THEN Lock transmitter. When these base stations receive the function code, they lock (disable) their transmitter, but continue as fill-in receivers. TaitNet P25 Conventional System Manual Channel Group Configuration 51

52 3. Set up equivalent Task Manager tasks to unlock the transmitters on receiving the appropriate function tone/function code. 4.8 Digital Fixed Station Interface Any base station or P25 console gateway can provide its channel group with a digital fixed station interface (DFSI). A DFSI feature license is required. A channel group can have more than one DFSI. Channel Control The DFSI supports the following dispatcher commands for channel control. Most commands need collective channel control (see Collective Channel Control on page 50) to coordinate them across a whole channel group. Dispatcher Command Monitor RF repeat enable/disable Change channel Voter control (select or disable receiver) Propagation of Command Collective setting Collective setting Collective setting Member with DFSI forwards command to channel group Monitor The dispatcher can send a monitor command in order to hear what is being received by the channel group. The monitor command disables checking for NAC and for subaudible signaling. If the channel group has collective control enabled, the monitor command applies to the channel group as a whole, not just to the member with the dispatcher interface. Monitor mode provides the dispatcher with one voice stream at a time. If the channel group is receiving more than one call, it provides the votewinning call; it cannot sum audio from multiple calls. If it receives a call with the correct NAC or subaudible signaling, that call wins the vote over any calls with incorrect NAC or subaudible signaling. In other words, the monitor command only makes a difference when valid calls are not being received. In monitor mode, channel group members still apply RSSI and/or SINAD gating to analog FM signals, if configured to do so. They do not feed lowlevel noise to the dispatcher. If a channel group with collective control receives a monitor command, it supplies monitored signals to any other dispatcher interfaces, not just to the interface that issued the command. If a dispatch console applies selective squelch, it needs to switch to normal squelch to hear the monitored signals. 52 Channel Group Configuration TaitNet P25 Conventional System Manual

53 RF repeat The dispatcher can enable or disable RF repeat. Channels in the channel table must be configured to put RF repeat under dispatcher control. If channel control is collective for RF repeat, the dispatcher command is implemented in all members of the channel group. To set up commands for enabling and disabling RF repeat 1. In the channel table of the member with the DFSI, set the RF repeat column to DispatchControlled. 2. For all channel group members, configure the channel group settings to have collective control of RF repeat. (Configure > Channel Group > Channel Groups and click Edit.) This ensures that the command is automatically coordinated across the channel group. Channel change The dispatcher can instruct the channel group to change to a particular channel number. If channel control is collective for this command, all members of the channel group change to that channel. Voter control The dispatcher can exercise control over the voting decisions of the channel group. If the dispatcher selects a particular receiver number, that receiver s voice stream always wins the vote. The other receivers are disabled. However, if the selected receiver is not receiving a call, channel group members can provide voice streams from their control panel or from another dispatcher interface. Alternatively, the dispatcher can send a command to disable a particular receiver. It then does not provide its RF voice stream to the voter(s). Subscriber signaling Digital dispatch equipment is able to provide subscriber signaling (individual ID, caller ID, group ID) over the DFSI. This signaling is embedded in the RTP voice stream. Digital dispatch equipment is also able to send and receive TSBKs. Unsupported DFSI Commands Change transmit channel/change receive channel The TB9100 base station and the P25 console gateway cannot separately change their transmit and their receive channel. Transmit channel change commands change the channel for transmitter and receiver. Receive channel change commands are acknowledged but have no effect. Intercom The optional intercom facility is not supported. Dispatchers and maintainers can use the normal voice service instead. TaitNet P25 Conventional System Manual Channel Group Configuration 53

54 4.9 Analog Line Interface An analog line provides the interface between a channel group and analog dispatch equipment. It can also interface to an analog FM base station or to call recording equipment. This interface is normally provided by a P25 console gateway, but if encryption/decryption is not required, it can be provided by a TB9100 base station. The base station needs an analog line feature license. Figure 4.2 Interfacing a channel group to a console system Digital P25 or analog FM Base station Base station IMBE or G711 IMBE or G.711 Base station IMBE or G.711 Linking Infrastructure Analog voice + channel control + subscriber signaling P25 Console Gateway IMBE or G.711 Base station Time Analog Console System Channel Control Dispatcher commands can exert channel control over the channel group. Control is exerted over all members of the channel group, not just to the member with the interface. Where needed, this is done through a collective setting. The following table summarizes the supported analog dispatcher commands and indicates the signaling methods that dispatch equipment can use to communicate these commands over the interface. It 54 Channel Group Configuration TaitNet P25 Conventional System Manual

55 also indicates whether the command needs to be propagated to all channel group members and whether a collective setting is available to enable this. Dispatcher Command E & M Available Signaling Methods Keytone (LLGT) Function Tone a Propagation of Command Tx Key (channel seize) Yes Yes Not needed Rx Gate (analog valid) Yes Not needed Select mode (analog FM/ digital P25) Yes Not needed Monitor Yes Collective setting Select encrypted/clear Yes Not needed RF repeat enable/disable Yes Collective setting Cancel P25 unit call Yes Not needed Change channel Yes Collective setting Wildcard (trigger TM action) Yes Function codes a. Function tones can be configured to select a calling profile, to implement the cancel P25 unit call command, or to trigger Task Manager actions. Tones are configured in the Tone Remote Mapping form (Configure > Analog Line > Tone Remote Mapping). Subsequent sections describe the signaling methods and dispatcher commands used for channel control and indicate how they are enabled and configured using the CSS. E & M signaling In a traditional analog system, the E & M lines are used for Rx Gate and Tx Key signals. Rx Gate tells the console system that the receiver has unmuted. Tx Key tells the base station to transmit. In a channel group, things are more complicated. An Rx Gate signal does not necessarily mean that the receiver has unmuted. It does indicate that there is a valid audio signal, but this might have been received by any channel group member or have come from the control panel microphone. Similarly, a Tx Key signal doesn t necessarily key the transmitter, as any incoming signal competes for selection with other signals. Accordingly, at the analog line interface, we use the terms Analog valid instead of Rx Gate and Channel seize instead of Tx Key. Analog valid indicates that there has been a selection and that it has been switched to the analog line out. Channel seize indicates that there is a signal on the analog line and asks the channel group to consider it for selection. To configure the E & M Lines for Analog valid and Channel seize 1. Select Configure > Analog Line > General. TaitNet P25 Conventional System Manual Channel Group Configuration 55

56 2. Under Channel seize and analog valid, select the E & M check box. Keytone Keytone (also known as LLGT low level guard tone) can convey a channel seize signal. This instructs the channel group member to present the audio from the analog line to the channel group for selection. If the audio is selected, it is transmitted by the base stations in the channel group. When the keytone stops, the channel group stops transmitting. To configure the detection of keytone 1. Select Configure > Analog Line > Tone Remote Options. 2. In the Guard tone frequency box, select the keytone frequency. 3. In the LLGT level box, select a minimum level for the keytone. In the HLGT level box, make sure that the level selected for high level guard tone exceeds the actual keytone level. 4. Enable the notch filter. To configure keytone as a channel seize signal 1. Select Configure > Analog Line > General. 2. Under Channel seize and analog valid, select Tone remote. 3. If MDC1200 signaling is used, select After MDC1200. This configures the channel seize to occur some time after LLGT begins, so that MDC1200 signaling is not included in the transmitted voice stream. Tone remote function tones The analog line supports the use of single and dual-tone tone remote signaling from console to channel group member. The tones are carried on the audio line in. The channel group member can respond to a tone remote function tone by selecting a calling profile or by carrying out Task Manager actions with that function tone as an input. Selecting a calling profile overrides the calling profile assigned to the current channel. Note Subscriber-related settings in the calling profile can be overridden by MDC1200 signaling. Tone remote signaling consists of a high-level guard tone (HLGT), followed by one or two function tones, then low-level guard tone (LLGT), accompanied by audio. 56 Channel Group Configuration TaitNet P25 Conventional System Manual

57 Figure 4.3 Tone remote signaling HLGT Function tone 1 Function tone 2 LLGT MDC LLGT Voice + LLGT ~ 600 ms To configure tone remote signaling 1. Adjust the parameters for detecting tone remote, so that they conform with the tones that the console system produces. 2. Create calling profiles and using the assign them to the tones that the console system will use 3. For commands that cannot be implemented using calling profiles, create channels in the channel table and use Task Manager tasks to select them when the appropriate tone is received. Select mode If the channel group supports both analog FM and digital P25 users, the dispatcher needs to be able to select the mode when initiating a call. Configuring the base station for Select mode commands is done by defining calling profiles, each with the required mode, then assigning function tones to those profiles. Selecting a calling profile not only assigns the mode, but many other properties of the analog line as well. This means that the dispatcher may need several different calling profiles (you can define up to 16). To set up commands for selecting analog FM or digital P25 modes 1. Set up calling profiles for the different modes: one for Analog FM and one for each group or individual that the dispatcher wants to call in digital P25 mode. 2. Assign the calling profile to be used as the default to the channel or channels that the base station will normally use 3. Assign the calling profiles to the function tones that the console system will use (Configure > Analog Line > Tone Remote Mapping) TaitNet P25 Conventional System Manual Channel Group Configuration 57

58 4. Make sure that the channel profiles assigned to the channel(s) that the base station uses support receiving both analog FM and digital P25 (otherwise the dispatcher will be able to talk to the radios but the base station will not be able to receive their reply). 5. Assign the function tones to suitable controls on the console system. Activating these controls will select the corresponding calling profile. Assigning a function tone that changes calling profile to the PTT button is not recommended, as the call cannot begin until the profile has been changed. Note When the console transmits in one mode, it can still receive calls in the other mode. To reply, the dispatcher must first select the mode used by the caller. Monitor A Monitor command disables checking for NAC and for subaudible signaling in all base stations in the channel group, if collective control is enabled. If a channel group in monitor mode receives a call with the correct NAC or subaudible signaling, that call wins the vote over any calls with incorrect NAC or subaudible signaling. In other words, the monitor command only makes a difference when valid calls are not being received. Monitor mode provides the dispatcher with a single call. If the channel group is receiving more than one call, it provides the vote-winning call; it cannot sum audio from multiple calls. In monitor mode, channel group members still apply RSSI and/or SINAD gating to analog FM signals. They do not feed low-level noise to the dispatcher. Monitor mode overrides any selective squelch that the current calling profile applies to the analog line. If the monitored call is encrypted and the key is present, the analog line provides the decrypted call. If the correct key is not present, the analog line provides encrypted voice. To set up commands for enabling and disabling monitor mode 1. Set up Task Manager tasks such as the following: IF Tone remote detected (550) THEN Enable monitor IF Tone remote detected (750) THEN Disable monitor 2. Configure all channel group members to have collective control of Monitor squelch (see Collective Channel Control on page 50). RF repeat The dispatcher can enable and disable the RF repeat function of the channel group. 58 Channel Group Configuration TaitNet P25 Conventional System Manual

59 To set up commands for enabling and disabling RF repeat 1. In the channel table of the member with the analog line interface, set the RF repeat column to DispatchControlled. 2. Set up Task Manager tasks such as the following: IF Tone remote detected (550) THEN Enable RF repeat IF Tone remote detected (750) THEN Disable RF repeat Even though a P25 console gateway cannot repeat, you need to provide it with these tasks for sending to members who can. 3. Configure all channel group members to have collective control of RF repeat (see Collective Channel Control on page 50). Cancel P25 Unit Call The dispatcher can cancel a P25 SU to SU call to free the channel for the dispatcher s own call. To set up a command for canceling a P25 SU to SU call In the P25 console gateway, Tone Remote Mapping table, map a function tone to the action Cancel P25 Unit Call. Note If the current calling profile has AutoReply enabled, the dispatcher can use this command to override the automatic replying to the sender of the previous call, so that the dispatcher calls the configured call destination instead. Change channel If the dispatcher needs to communicate with users on a different frequency pair, or to change other operating parameters of the base stations in the channel group, the base stations can be configured to respond to a dispatcher command by changing channel. This is done through Task Manager. To set up a command for changing channel 1. In the P25 console gateway, create a Task Manager statement with the function tone as input and a change channel command as action. For example: IF Tone remote detected (550) THEN Go to channel Configure all channel group members to have collective control of the channel number (see Collective Channel Control on page 50). Note The dispatcher should not use the change channel command when the base station is transmitting. The change to the new channel s calling profile will not take place until the analog line initiates a new transmission. TaitNet P25 Conventional System Manual Channel Group Configuration 59

60 Subscriber Signaling Subscriber signaling is passed over the analog line mostly as MDC1200. However, function tones can be used to select calling profiles for digital P25 calls that specify an individual or group address and a sender ID. The analog line supports the use of MDC1200 (also known as Stat Alert) for subscriber signaling. In analog FM mode, the channel group passes MDC1200 transparently between dispatch console and radio and also between radios. No configuration is required. In P25 digital mode, the analog line can convert MDC1200 signaling to P25 signaling and vice versa. This enables analog console systems to make use of P25 features that are unavailable to tone remote signaling. The other base stations in the channel group do not need to be configured; the P25 signaling is propagated as part of the voice stream. The channel group member with the analog line requires the following: MDC1200 feature license MDC1200 signaling must be enabled (Configure > Analog Line > General. Select the MDC1200 check box) Each required MDC1200 feature must be enabled MDC1200 addresses must be mapped to P25 IDs. Generally, the default mapping is sufficient Many MDC1200 messages require an acknowledgement and can be retried until an acknowledgement is received. The number of retries is determined by the console system. The retry rate, also determined by the console system, may need to be reduced to take account of the slower response when the message and its response need to be converted to and from digital P25. The following sections describe the MDC1200 signaling messages that are supported in digital P25 mode. They also provide configuration instructions. Caller identification (ANI) The most common use of MDC1200 signaling is to provide the called party with the identity of the caller. In analog systems, radio equipment can send a MDC1200 message containing the ID of the caller. This ID can be displayed on the receiving radio or console system. The feature is known as ANI (automatic number identification) or PTT ID. Console systems can also send ANI messages. In digital P25 mode, the TB9100 can take the source ID of an incoming P25 call, convert it into a MDC1200 ANI message with an equivalent MDC1200 address, and send it to the dispatch console. For outgoing calls, the analog line uses the line ID specified by its current calling profile as its ANI. 60 Channel Group Configuration TaitNet P25 Conventional System Manual

61 To configure the analog line for caller identification on incoming calls 1. If possible, set up the analog line for trailing ANI (Configure > Analog Line > General). This adds the ANI message at the end of the over, reducing the delay at the start of the over). 2. If desired, modify the default mapping of P25 addresses to MDC1200 addresses (Configure > Analog Line > MDC1200 Address Table). This mapping converts the source addresses of digital P25 calls it receives into equivalent MDC1200 ANIs. To configure the dispatcher s caller identification 1. Assign the the dispatch console an MDC1200 address in the range Enter the same number into the Line ID box of all the analog line s calling profiles. (This assumes the default mapping in the MDC1200 Address Table. You are entering a decimal P25 address that the address table converts into the console s hexadecimal MDC1200 address.) The line ID will be used as the console s caller identification on outgoing digital P25 calls. Note Many radios will send status messages to a dispatcher ID that is derived from the talk group they currently belong to. You don t need to configure the analog line for these messages. The base station automatically switches them onto the analog line, if the current group membership includes the talk group. The MDC1200 destination ID is calculated from the calling profile s Line ID and not from the actual destination ID of the status messages. Emergency ANI This is similar to ANI, except that the message format is slightly different and the associated call is an emergency call. Outbound calls: When the analog line receives a MDC1200 emergency ANI message, it makes the following call an emergency call (overriding the setting in the current calling profile). Inbound calls: When the channel group receives a P25 emergency call, the analog line produces an MDC1200 emergency ANI message. Additional services MDC1200 can also be used to provide a range of services additional to ordinary voice calls. If these are to be converted to or from their digital P25 equivalent, the current service profile must enable them. Messages on the analog line (in MDC1200 format) must be enabled in the service profile attached to the calling profile. Messages arriving from a receiver in the channel group must be enabled in the service profile attached to the current channel of the base station receiving the message. TaitNet P25 Conventional System Manual Channel Group Configuration 61

62 Call alert The dispatcher can send a call alert message to a radio. The radio acknowledges the message and may provide a tone or LED indication that the user is to call back. The radio sends a call alert to the dispatcher, if the service profile assigned to the current channel enables it. The base station can convert a MDC1200 call alert message into a P25 call alert supplementary service and vice versa. Radio check The radio check message lets the dispatcher test whether a radio is powered up and within coverage. Emergency alarm The dispatcher can receive an emergency alarm message from radios. This is also known as emergency alert or man down. Receiving this message may cause an alarm indication on the console system. No base station configuration is necessary for this message; it is not possible to disable this function. Radio disable/radio enable The dispatcher can disable or enable radios (P25 refers to this as inhibit or uninhibit), provided the radios support the feature and have it enabled. Remote monitor The dispatcher can remotely monitor P25 radios on the network. The console system sends the MDC1200 message, which is converted to the equivalent P25 message. The individual address of the radio is converted from MDC1200 to P25 format. Status update and status request The dispatcher can request status information from a radio and the radio can send an update on its status. Call addressing (voice alert) MDC1200 voice alert messages have been used in analog systems for some time to address calls to particular individual radios or groups. The analog line can turn this into a P25 individual call to the equivalent P25 individual or group, overriding the setting in the calling profile. The default mapping between MDC1200 and digital P25 addresses can be displayed in the CSS and suffices for most purposes. Function Tone Subscriber Signaling Where MDC1200 is not available, a dispatcher can use function tones to provide a limited capability for subscriber signaling in digital P25 mode. The function tones select a calling profile that specifies a destination group or individual ID. Calling groups To set up a command for calling a group 1. Set up a calling profile and select the call type P25 group. Enter the group ID in the Destination field. 62 Channel Group Configuration TaitNet P25 Conventional System Manual

63 2. Set up a group membership with that group included. This ensures that the dispatcher can listen to the group. 3. Select Configure > Analog Line > Tone Remote Mapping and assign the calling profile you created to the function tone that the console produces when the button is pressed. Calling individuals There is a limited ability to use tone remote signaling to make calls to an individual ID. A calling profile is needed for each individual ID and only 16 calling profiles are available for individual and group calling. To set up a command for calling an individual 1. Set up a calling profile and select the call type P25 individual. Enter the individual ID in the Destination field. Note: the analog line will automatically listen to calls addressed to the Line ID in the calling profile. 2. Select Configure > Analog Line > Tone Remote Mapping and assign the calling profile you created to the function tone that the console produces when the button is pressed. TaitNet P25 Conventional System Manual Channel Group Configuration 63

64 5 Network Design The following describes various aspects of the design of conventional TaitNet P25 networks: Elements comprising the network Network topology Factors to consider when designing channel groups Determining the required linking capacity Designing simulcast networks Using Task Manager scripts to implement customer-specific requirements Using TB9100s for RF linking Connecting a TaitNet P25 network to the organization s own network via a firewall Enabling remote access and support by Tait engineers Making the transition from an existing analog system 5.1 Network Elements A TaitNet P25 network consists of various network elements: Tait products (the TB9100 base station and the P25 console gateway) and off-the-shelf network equipment (switches, routers, and hubs). Only Tait-approved equipment should be used. It must support particular features such as multicast, VPN, proxy ARP, and IGMP. Trunked networks also have two or more trunking site controllers. The network can interface to third-party dispatch equipment and voice recorders. The Tait network elements are modular. Different models consist of various combinations of modules. For more information about module combinations, see the TB9100/P25 CG Installation and Operation Manual. In addition, there is a variety of optional features, each requiring a software feature license. All Tait network elements have at least one channel module. For a base station, this is a reciter (an RF receiver/exciter). For a P25 console gateway, this is a gateway module. 64 Network Design TaitNet P25 Conventional System Manual

65 TB9100 Base Station The TB9100 base station is available as single-channel and dual-channel subracks. Receive-only base stations can have up to five receive channels (or seven receive channels, if there is no power management unit) in a single subrack. TB9100 base stations have many capabilities that require enabling by feature license. P25 Console Gateway P25 console gateways have a digital line (IP over Ethernet to connect to the network) and a 4-wire E & M analog line to connect to the console equipment. Their encryption capabilities are similar to Tait P25 mobiles and portables. They can store up to 16 encryption keys. The DES and AES algorithms are supported. The P25 console gateway has a standard P25 key-fill interface for loading encryption keys. This can be done using the Motorola KVL3000+ key fill device. P25 console gateway operation can be monitored and configured using the same CSS as is used for the TB9100 base station. Currently, the P25 console gateway consists of a TB9100 reciter with the receive and transmit functions disabled. 5.2 Topology TaitNet P25 networks normally use a star topology. This means that there is a maximum of two hops between any two members of a channel group. Multiple physical links can be provided between routers or switches to provide redundancy. It is also possible to have a second central router in position, to remove the single point of failure. Non-star configurations are acceptable for switched networks. Although there are more links, the latency on each link is much lower, so that the absolute jitter is still low. Non-star topologies such as mesh and ring are not recommended for routed networks. The increased number of hops increases latency and jitter. These topologies provide alternative data routes, which may result in packets being received out of order. Base stations drop these packets and substitute empty values for them, resulting in a loss of audio. TaitNet P25 Conventional System Manual Network Design 65

66 5.3 Channel Group Design Factors The following factors need consideration to ensure that a channel group functions effectively. Number of Members A channel group can have up to 14 members, if sufficient linking bandwidth is provided, and the network delay is sufficiently small. Preamble Length The length of the call preamble is important in scan/vote systems. Preamble is a standard high-deviation test pattern that a base station transmits at the beginning of each call, while the transmit buffer is filling. The transmit buffer can hold up to 300ms of signal. The Preamble box in the Edit Channel Group dialog box defines the length (duration) of the preamble. Tait SUs use the preamble to scan the available channels, vote on them and switch to the best one. In 300ms, they are able to scan three channels. If the channel group has more than three transmitters, an SU may still be scanning when the preamble ends, so that it misses the call header and enters the call late. This risk can be reduced by configuring SUs for fast vote and by minimizing the differences in transmitter launch time, so that the SU synchronization time period can be set low. Using these methods, channel groups with scan/vote can have up to 10 transmitters and still keep late entry to an acceptable level. Marshalling Duration The marshalling duration is the amount of time needed for the voice stream to travel from the central voter to the most distant transmitter (the one with the most router or switch hops). The maximum marshalling duration is 150ms. Simulcast channel groups need to be designed so that the network delay for the path from the central voter to any simulcast transmitter is not greater than 150ms. Central Voter Arrival Time Skew In centrally voted channel groups, an SU call can result in several voice streams. There is a time difference between the arrival at the central voter of a packet from one base station and the equivalent packet from another base station. This time difference is called skew. In the diagram below, SU d makes a call which is received by the central voter and by base station B. The network delay for the path from B to the central voter is 120ms, so the voice stream from B arrives with a skew of 66 Network Design TaitNet P25 Conventional System Manual

67 120ms. This exceeds the maximum skew (100ms) that the central voter can handle, so it discards the voice stream. However, signals from SUe, which are received by B and C, will be voted on, because the skew for the stream from C is 80ms. d e Central voter 120 ms B 80 ms C Expressed in general terms, the network delay for the path from a base station to the central voter can exceed 100ms, but the difference in delay between base stations with overlapping coverage cannot. In the example above, the difference in network delay between B (120ms) and the central voter (<10ms), and between C ( ms) and B (120ms) needs to be 100ms or less. 5.4 Simulcast Providing a 1PPS Signal In a simulcast network, each site needs an external frequency reference and 1PPS signal. This can be provided to all transmitters at a site by a single Tait T801-4 GPS frequency reference. Cabling must minimize signal delay and suppress reflections. For details, see the T801-4 Installation and Operation Manual (MBA xx). Minimizing the Delay Spread Problem Careful attention must be paid to the design of each simulcast channel group, so as to minimize the delay spread problem and its associated areas of degraded performance. A propagation prediction tool (such as EDX SignalPro, see can help identify these areas. Tait SUs are able to measure BER and can be used in installation and commissioning to check that the measures taken to minimize delay spread are effective. The delay spread problem The diagram below is a simplified model of a two-site simulcast system, illustrating how the delay spread between signals from different transmitters can cause areas of degraded performance. TaitNet P25 Conventional System Manual Network Design 67

68 50 Degraded performance Degraded performance Vertical distance from origin (km) 0 A Capture boundary B Delay spread boundary 0 50 Horizontal distance from origin (km) Base stations A and B are shown as black dots and the blue and red dashed circles around them show the ordinary downlink range of their transmissions. The solid green lines mark the boundary where the signal from the nearer base station is sufficiently stronger than the signal from the further base station to ensure good reception. The nearer base station is said to capture the SU. The longer, dashed blue lines mark the delay spread boundaries. Between these lines, the delay spread of the signals from A and B is small enough for SUs to cope. On the other side of the lines, the delay spread is too great, resulting in degraded performance. Note that the delay spread problem is not at its worst in the middle of the overlap zone. Rather, half-way between the base stations, the delay spread is 0, as both signals travel the same distance.the delay spread problem is in two bands on either side of that middle position. These can be seen as areas of increased BER, as shown below. BER - 50 Horizontal distance from origin (km) Network Design TaitNet P25 Conventional System Manual

69 Bear in mind also that the capture effect is not a sudden, all-or-nothing matter. As the power difference between the signals increases, the BER reduces. The task of designing a simulcast system involves eliminating, reducing, or moving these areas of degraded performance. If the delay spread boundary is moved to the capture boundary, the area of degraded performance disappears. The following methods are available. Reducing the distance between sites Using a modulation scheme designed for simulcast Delaying launch times Adding a carrier frequency offset Moving base sites closer together can eliminate the regions of degraded performance. However, this also reduces the total geographical area covered by the system. The impact of this can be the need to use extra base sites which is clearly very expensive. If the simulcast system uses the TSM modulation scheme for the downlink, we recommend using 39µs as the design value of the delay spread. This equates to a site separation of 12km without areas of degraded performance (assuming that you are designing to a 2% BER (3.4 DAQ)). It compares favorably with 27µs for C4FM. (While the TIA standard TSB 88 suggests a peak delay spread value of 33µs for C4FM, various system losses need to be allowed for.) Where degraded regions cannot be eliminated, they can be moved to locations that do not require coverage, for example over a body of water. Delaying the launch time of one transmitter compared to another shifts the degraded regions. If this moves a degraded region inside a capture boundary, the degradation is removed. Altering the transmit power (or antenna gain) of a site can shift the capture boundary, and have a similar effect. Using the CSS, you can delay the launch time (the local transmit offset) of an individual transmitter in increments of 1µs, each of which corresponds to a shift of around 150m. Small adjustments to the carrier frequency can be made. In theory, there could be static nulls (places where the signals from two or more transmitters cancel each other out). Adding a carrier frequency offset would cause these nulls to move. We suggest using a carrier offset of 4-5Hz, to prevent the occurrence of static nulls. Experience shows that small carrier frequency differences make practically no difference to the observed BER. Using the CSS, you can configure a carrier offset in increments of 1Hz. Differential Doppler Effects When a mobile or portable radio is moving at speed towards one base station and away from another, it receives signal from one base station at an increased frequency and from the other at a decreased frequency. This is known as differential Doppler. If the radio is in an area of high delay spread, downlink performance is degraded. The effect is worse at higher transmit frequencies (800 MHz). In some circumstances, the network design may be able to mitigate the effects by positioning sites away from high-use areas, so TaitNet P25 Conventional System Manual Network Design 69

70 that vehicles are not traveling directly towards or away from sites. Otherwise, it may be necessary to design the system for a lower delay spread. 5.5 Linking Capacity Once the network topology has been decided upon, the bearer network needs to be provisioned with sufficient IP capacity to reliably carry voice traffic, even in the presence of other IP data. This section identifies the variables that affect the load on the network and gives some rules of thumb to assist network designers to adequately estimate a suitable linking capacity. The end result will involve a trade-off between cost and quality of service. Variables The following variables affect the loading on the network. Calling types P25 calls require less network bandwidth than FM calls. P25 calls use an IMBE vocoder to reduce the raw speech bit rate. The vocoder data rate is 4.8kbit/s. With the addition of P25 framing information, IP network framing overhead and voting information, the data rate increases to approximately 15kbit/s. FM calls are converted to the G.711 format for transmission on the network. The basic data rate of G.711 is 64kbit/s and it therefore requires significantly more linking capacity. Voting type If there is no common uplink frequency, receivers are assumed not to be listening to the same signal and the channel group is configured with the voting type switched. If two SUs begin overs at the same time, there is a single transient load spike at the beginning of the over as the receivers choose which SU to handle. This single load spike can be disregarded when estimating linking capacity. If voting is centralized, voice streams are sent from multiple receivers to the central voter. The capacity requirement is well-defined. If voting is distributed, several voice streams can be on the network simultaneously, causing transient load spikes throughout the over. Although most of the time the load is low, linking capacity must be sufficient to handle these spikes. Estimating this capacity is more difficult. Simplex/duplex channel group A channel group can be simplex or duplex. When the channel group is duplex, each member votes separately on two voice streams: inbound (from RF to the dispatcher) and outbound (from the dispatcher to RF). A base station in a duplex channel group is capable of sending one stream and receiving another stream over the digital line at the same time. However, if it also has a dispatcher interface, it must be capable of sending two streams simultaneously; one from its RF interface and the other from the dispatcher interface. 70 Network Design TaitNet P25 Conventional System Manual

71 Network delay Increasing the network delay also increases the load on network links in systems with distributed voting. The network design should aim to minimize the network delay. Network topology Having more than two hops in a network adds to the network delay. Tait strongly recommends using a Star topology. For centralized voting, the star topology is necessary. The figures and calculations below are based on a Star topology, which has no more than two hops. Linking Options To keep the linking capacity to an absolute minimum, use routers and configure them with compressed RTP (CRTP). If you use routers, configure them for QoS support. If linking capacity is plentiful, use switches instead of routers. They are easier to set up, operation under load is more predictable, and they minimize network delay. Facility Description Advantages Disadvantages Compressed RTP Compress the IP packets containing voice Reduces the network load to an absolute minimum Requires CISCO routers Can be complex to set up Less predictable Does not scale to large networks (> 20 channel groups) Cannot be used with links of 2Mbit/s and beyond QoS support Prioritize the real-time (voice) stream ahead of other traffic Minimal additional delay when other traffic is present Requires routers Switches Use a VLAN without routers. No other traffic shaping required. Network is simple and predictable Delays are minimized Cannot use QoS and so must over-provision to accommodate non-voice traffic Determining the Number of Voice Streams To estimate the required network bandwidth, you need to determine the maximum number of simultaneous voice streams that the links between sites must be able to carry. The number of streams from the central switch or router to the network element (HQ) at the center of the star topology is not of interest, provided that the link is Ethernet (high bandwidth). HQ can be a P25 console gateway, a base station, or a base station with a digital dispatcher interface. The following discussion assumes that the dispatch equipment interfaces to the network element at the center of the star topology. If it interfaces to TaitNet P25 Conventional System Manual Network Design 71

72 another network element, that element s link may need to handle more streams. The following diagram shows the streams that appear on intersite links when an SU makes a call in a channel group with four members. BS3 Switch BS1 Switch Central Switch Switch BS2 HQ Switched. In systems where the voting type is switched, there only needs to be sufficient capacity to handle a single voice stream in any one direction. Any base station (BS1 in the diagram below) can provide a subscriber stream to the network and at the same time receive a dispatcher stream. BS3 BS1 HQ BS2 (There is an exception to this rule: In duplex channel groups, if a channel member has a RF and a dispatcher interface, it can have two outgoing voice streams: one from the receiver and the other from the analog line or DFSI.) 72 Network Design TaitNet P25 Conventional System Manual

73 Central Voting. When voting is central and the channel group is duplex, links to the central voter can have one incoming and two outgoing streams. (While the Ethernet link from the central switch or router to the central voter carries one incoming stream from each active receiver, each link into the central switch or router only has one incoming stream.) BS3 BS1 Central voter BS2 If the channel group is simplex, the central voter only has one outgoing stream. However, if a channel member has a RF and a dispatcher interface, it can send two streams to the central voter. Distributed Voting. When voting is distributed among the members of the channel group, there are transient load spikes in which there can be more than one voice stream on a link at the same time. Each additional simultaneous receiver adds a voice stream to the outgoing link. In the following example, three base stations in the channel group are simultaneously receiving the same signal. BS3 This link needs capacity for up to 2 incoming and 1 outgoing streams BS1 HQ BS2 Note that there is only one outgoing stream, but n-1 incoming streams, where n is the number of simultaneous receivers. The P25 console gateway is an exception, having n incoming streams. TaitNet P25 Conventional System Manual Network Design 73

74 If the system is duplex, there is an additional stream originating from the dispatcher: BS3 BS1 Outbound HQ Outbound Outbound BS2 Time The following table indicates the number of voice streams involved for different scenarios in voted systems. Channel Group Type Link Number of Voice Streams Two Receivers Three Receivers Simplex Incoming 1 2 Outgoing 1 1 Duplex Incoming 2 3 Outgoing 1 1 Incoming to P25 console gateway a 2 3 Outgoing from P25 console 1 1 gateway a Incoming to base station with DFSI a 1 b 2 b Outgoing from base station with 2 2 DFSI a a. This is relevant only when the network element is not positioned at the center of the star topology. b. Assumes that the base station is one of the receivers 74 Network Design TaitNet P25 Conventional System Manual

75 Estimating the Link Capacity Requirement If the linking capacity needs to be kept to a minimum, use the following section to estimate the requirements. This is fairly straightforward for nonvoted and centrally voted systems, but more complex for systems with distributed voting. Step 1: Determine the bandwidth of the voice stream The following are estimates of the capacity requirement for each type of voice stream. Call Type Compressed RTP RTP Digital P kbit/s 54kbit/s Analog FM 100kbit/s 120kbit/s Step 2: Adjust for the number of voice streams To estimate the total capacity required by the voice streams 1. Determine the maximum number of voice streams (see Determining the Number of Voice Streams on page 71) 2. Multiply the allowance for the voice stream (Step 1) by this number. Step 3: Add an allowance for administrative traffic The basic requirement for the voice stream includes an allowance for maintenance traffic (alarms, configuration, monitoring). This is generally sufficient for routed networks. These have QoS, which prioritizes speech traffic. Lower-capacity links may need additional bandwidth to handle this traffic. Switched networks do not have QoS and therefore need an allowance for maintenance traffic, as follows: Service CSS monitoring Syslog messages to collector (Trace level) Syslog messages to collector (Notice or Warning level) Additional allowance 23kbit/s (per CSS) 16kbit/s (per base station) 5kbit/s (per base station) Step 4: Combine the estimates for each channel group To estimate the total capacity for each mono-directional link: Add together the capacity that you estimated separately for each channel group TaitNet P25 Conventional System Manual Network Design 75

76 Example Calculations The following provide two example calculations resulting in capacity requirements for one channel group. Centrally voted system The channel group is duplex. The network is routed and without CRTP. Calls are P25 only. Voice stream base capacity (Step 1) = 54kbit/s Maximum number of voice streams (incoming): = 1 (Step 2) Maximum number of voice streams (outgoing): = 2 (Step 2) 108kbit/s is the linking capacity requirement for the channel group for each mono-directional link. Simplex system with distributed voting The channel group is simplex. The network is routed and without CRTP. Calls are P25 only. There can be up to three simultaneous receivers. Voice stream base capacity = 54 (Step 1) Maximum number of voice streams (incoming): = 2 (Step 2) Maximum number of voice streams (outgoing): = 1 (Step 2) Allowance for administrative traffic = 0 (Step 3) Linking capacity requirement (incoming streams): = 2 x 54 = 108kbit/s Linking capacity requirement (outgoing streams): = 1 x 54 = 54kbit/s 5.6 Task Manager Scripting Task Manager is a powerful tool enabling network designers to customize the design of a network in order to implement specific customer requirements. This section provides some tips on how to use Task Manager followed by examples showing how quite complex functions can be implemented. 76 Network Design TaitNet P25 Conventional System Manual

77 Scripting Tips The dispatcher can trigger any desired Task Manager action by pressing a wildcard button. This button causes the console to send a particular function tone to the connected base station or P25 console gateway. A SU can trigger any desired Task Manager action by sending a NAC. Task Manager can instruct a TB9100 base station to send a function code that functions as a heartbeat (a message indicating that the base station has not failed). To implement a heartbeat, configure a Task Manager timer to start on entering Run mode. Create tasks that send a function code and restart the timer when the timer expires. Task Manager can lock (disable) the transmitter of a back-up base station and unlock (enable) it when it is needed. Task Manager flags can be set up to represent the state of the base station, another base station, or the channel group (for example, standby, active, other base station unavailable, in fallback mode). Task Manager can control digital outputs to indicate the state of the base station to external equipment. Task Manager can instruct the base station to operate on a different channel, which can define quite different base station behavior. Example 1: Joining and Splitting Channel Groups The Police Department has a 4-site network of UHF base stations, one at each site. The Fire Department has a network of four VHF base stations, located on the same sites and using the same IP infrastructure. Normally, the police and fire networks operate separately, but they want to be able to work together sometimes, for example during major emergency events. Fire channel group Fire Police VHF 1 VHF 2 VHF 3 VHF 4 Digital I/O UHF 1 UHF 2 UHF 3 UHF 4 IP connection Police channel group Site 1 Site 2 Site 3 Site 4 In normal mode, police and fire belong to separate channel groups. Voting selects the best police signal and the best fire signal for repeating within each channel group. TaitNet P25 Conventional System Manual Network Design 77

78 During emergency mode, the fire base stations join the police channel group. Police and fire personnel can easily communicate with one another. Talkgroups can still be used to divide personnel into teams if there are too many to be all-informed. Any SU user can switch the operating mode. Sending NAC 29F causes the fire base stations to join the police channel group. The base station receiving the NAC communicates the message to VHF 2, which instructs the members of its channel group to change to channel 2, which specifies the channel group that the UHF base stations belong to. Splitting the channel group proceeds in a similar way. An SU user sends NAC 24E. The message is passed on to VHF2, which instructs the other VHF base stations to change back to channel 1, which specifies the fire channel group. Switching operating mode The command to switch operating mode is handled differently, depending on which base station receives it. The following diagrams show in detail how this is done for the command to switch back to separate channel groups. VHF 2 receives If VHF 2 receives the NAC that the SU user sent, it sends function code 14, instructing the other fire base stations to change back to the channel that specifies the fire channel group. 24E VHF 1 UHF 1 VHF 2 UHF 2 VHF 3 UHF 3 Function code 14 Send function code Function code 14 Go to channel 1 (Normal mode) Go to channel 1 and toggle digital I/O Detect I/O toggle Set digital I/O = 00 Go to channel 1 (Normal mode) Another VHF base station receives If another VHF base station receives the NAC, it sends function code 11 to VHF 2, which sends function code 14 to its channel group. 78 Network Design TaitNet P25 Conventional System Manual

79 24E VHF 1 UHF 1 VHF 2 UHF 2 VHF 3 UHF 3 Send function code Function Code 14 Go to channel 1 (Normal mode) Function Code 11 Send function code Function Code 14 Go to channel 1 and toggle digital I/O Detect I/O toggle Set digital I/O = 00 Go to channel 1 (Normal mode) A UHF base station receives For UHF base stations to handle the switch command, signaling between the VHF and UHF base stations is needed. This is done via the digital I/O that links VHF 2 and UHF 2. UHF2 VHF2 Dig Out 1 Dig In 0 GND Dig Out Bit 1 Reset Bit Dig In 0 GND Dig In 1 Dig Out 0 UHF 2 s digital output 0 provides bit 0 and digital output 1 provides bit 1. The two bits have the following meaning: 00 = default (no change required) 01 = request change to normal mode 11 = request change to emergency mode VHF2 acknowledges when the change has been made by toggling its digital output 0. When this occurs, UHF2 resets its digital outputs to 00. UHF 2 receives When UHF 2 receives the NAC, it sets its digital outputs appropriately, telling VHF 2 to instruct the VHF base stations to revert to normal mode. TaitNet P25 Conventional System Manual Network Design 79

80 24E VHF 1 UHF 1 VHF 2 UHF 2 VHF 3 UHF 3 Function Code 14 Send function code Set digital I/O = 01 (Request normal mode) Function Code 14 Go to channel 1 (Normal mode) Go to channel 1 and toggle digital I/O Detect I/O toggle Set digital I/O = 00 Go to channel 1 (normal mode) Another UHF base station receives When another UHF base station receives the NAC, it sends function code 1 to UHF 2, which sets its digital outputs. 24E VHF 1 UHF 1 VHF 2 UHF 2 VHF 3 UHF 3 Receive special NAC Go to channel 1 (Normal mode) Send request to change to Normal mode Function Code 14 Function Code 1 Set Digital I/O = 01 Request normal mode Send request for Function Code 14 Normal mode Go to channel 1 and Go to channel 1 toggle digital I/O (Normal mode) Detect I/O toggle Set digital I/O = 00 This design can be enhanced by a heartbeat and by providing confidence tones. The heartbeat enables a VHF base station that did not see the initial change mode request to subsequently join the others. VHF 2 sends a function code to the channel group once per second. The VHF base stations reset their watchdog timer each time this heartbeat message is received. If a VHF base station is in the wrong mode, its watchdog timer expires, causing it to change to the other channel. 80 Network Design TaitNet P25 Conventional System Manual

81 The UHF transmitters can provide confidence tones by sending a burst of CWID to indicate that the operating mode has changed. (Subscriber units must be listening in dual mode, as CWID is an analog FM signal.) Example 2: Fallback Mode The provider of a network used by police and other authorities requires that the network can still operate if the Police Department s microwave link fails. Site 1 Police Department S S S Site 2 During normal operation, the console gateways at the Police Department function as fill-in receivers and do not transmit. If the link fails, the fill-in receivers at the police department enable their transmitters and begin functioning as if they were SUs. This is referred to as standalone mode. The other sites will repeat their calls. If the link fails, the dispatcher sends a function tone. When the fill-in receiver receives this tone, Task Manager enables its transmitter and changes to a channel that has the same transmit and receive frequencies as an SU. This channel also defines the calling profile (personality). The fill-in receiver then transmits any calls that the dispatcher makes and the other sites repeat them. TaitNet P25 Conventional System Manual Network Design 81

82 Example 3: Backup Channels The provider of a three-site network used by police and other authorities requires that the network can still operate if a site or an inter-site microwave link fails. The main site and the secondary site have several back-up base stations. Sites are joined by microwave links. Each site has an Ethernet switch. Secondary site Link B Police Department S Link A S Main site The network provider wants the following fallback options: If the main site fails, the back-up base stations at the secondary site come into service If link A fails, the back-up base stations at the secondary site come into service If the secondary site fails, the back-up base stations at the main site come into service Dispatchers can manually initiate the switch to any of the above options The desired behavior was implemented in the following way: Each base station sends a function code every second to the other members of its channel group. This functions as a heartbeat and also indicates the status of the channel at that site. (There is a different function code for each status.) Standby base stations have their transmit function disabled on entry into Run mode. Their receivers are operational and participate in voting. When a standby base station receives a function code indicating that the other site has failed, Task Manager enables the transmit function. Each base station has a number of flags indicating the current status of the other base stations in its channel group. Task Manager sets and clears these flags when it receives a function code that signals a change in status. If the dispatcher wants to switch manually to or from a backup option, the console sends a function tone which the fill-in receiver turns into function codes that represent commands to implement the desired option. 82 Network Design TaitNet P25 Conventional System Manual

83 5.7 RF Linking An ordinary RF voice channel can be used to link a channel group to a remote TB9100 base station or to a mobile dispatch center. In TaitNet P25 networks, this RF linking is provided by TB9100s especially configured for the task. They are referred to as linking transceivers. RF linking can be a cost-effective solution in areas where an IP-based infrastructure is not present or would be expensive to provide. Base station Linking transceiver Linking transceiver Base station Main channel group Remote channel group Local site Remote site It may be possible to use an ordinary TB9100 base station, functioning as a repeater, as one end of the link, with significant savings in equipment cost: Base station Main channel group Linking transceiver Base station Local site Remote site Uses and Limitations RF linking can be used for the following applications: Extending the coverage area of a channel group. RF linking connects a remote base station to the channel group. (The remote base station s coverage could in turn be extended by adding fill-in receivers or even additional base stations.) Giving a mobile dispatch console access to a channel group. RF linking connects a DFSI interface or analog line interface to the channel group. TaitNet P25 Conventional System Manual Network Design 83

84 RF linking has the following limitations. It does not support remote CSS connections. You cannot remotely connect a CSS to base stations on the other side of the RF link. Any configuration change or firmware upgrade requires a site visit. It cannot be used in analog FM mode. It is not suitable for joining channel groups if both of them have line interfaces as well as RF interfaces. It performs better with switched or distributed voting than with central voting. It can be used in simulcast systems, but the remote channel group cannot be synchronized to the main channel group. It may give unpredictable results if a maintainer uses the control panel at the remote location. It must use a specific NAC configuration, if one end of the link is an ordinary base station/repeater. A linking transceiver cannot provide an analog or DFSI line interface. Determining Site Suitability Each linking transceiver needs to receive a strong enough signal to provide an adequate fade margin. The TB9100 has the following P25 static sensitivity values (see also the TB9100 / P25 CG Specifications Manual). Use them to determine the suitability of the site locations and equipment for an RF link. Signal Strength Sensitivity Degradation BER DAQ dBm 0dB 5.0% -119dBm 1.5dB 2.6% dBm 2.0dB 2.0% dBm 3.0dB 1.0% 4.0 Configuration Overview The following lists the main configuration tasks needed for a pair of linking transceivers for each of the above applications. Dispatcher interfaces to main channel group When the dispatcher interfaces to the main channel group and the remote channel group is used as a coverage extender, there are normally a pair of linking transceivers. 84 Network Design TaitNet P25 Conventional System Manual

85 Base station Linking transceiver Linking transceiver Base station P25 Console Gateway Remote site Time Configure the system as follows. 1. Give each linking transceiver (and the other members of its channel group) a unique receiver number. This is essential to stop endless loops over the link. 2. Configure the remote base station as an ordinary repeater/channel group member. 3. Decide on the voting type and configure the members of both channel groups accordingly. Choose switched or distributed if possible. If you need to choose central voting, configure the remote channel group with switched or distributed. 4. Enable and configure RF linking, as follows. a. In the RF linking form (Configure > RF Interface > RF Linking), select the Linking transceiver check box. b. In the Link stream source box, select the source type that will be assigned to streams that the TB9100 produces from calls it receives on its RF interface. If the TB9100 is the local transceiver, select Subscriber. If the TB9100 is the remote transceiver (connected to the remote base station), select Dispatch. c. If the TB9100 is the local transceiver, enter into the Link speech impairment box a value between 0 and 15. This gives the received voice streams a fixed impairment value. Enter a low value if you want the link stream to normally win the vote or be selected in preference to calls from SUs at the main channel group. Enter a high value if you want the link stream to normally lose the vote or not be selected. d. If the TB9100 is the remote transceiver, the Link speech impairment box has no effect. The impairment value is not used when selecting dispatch voice streams. TaitNet P25 Conventional System Manual Network Design 85

86 e. If the TB9100 is the remote transceiver, leave the Allow loopback box cleared. If it is the local transceiver, and it should repeat RF signals that it has received over the RF link, select Allow loopback. 5. Enable RF repeat for each linking transceiver, regardless of the setting of other members of its channel group. 6. Set the preamble length based on the jitter on the linking transceiver s IP link. 7. Decide whether the linking transceivers will use specific NACs or whether they receive any NAC and transmit the NAC in the voice stream, and program them accordingly. Dispatcher interfaces to remote linking transceiver When the RF link is used to give a mobile dispatch console access to a channel group, there is normally only a single base station at the remote location. Base station Linking transceiver Base station Main channel group Time Local site Remote site Configure this system as follows. 1. Give the linking transceiver and all base stations a unique receiver number. 2. Decide on the voting type and configure the members of the main channel group accordingly. Choose switched or distributed if possible. If you need to choose central voting, configure the remote transceiver with switched or distributed. 3. Enable and configure RF linking in the local transceiver, as follows. a. Enable RF repeat (regardless of the setting of other members of its channel group) b. In the RF linking form (Configure > RF Interface > RF Linking), select the Linking transceiver check box. c. In the Link stream source box, select the Dispatch source type. d. Leave the Allow loopback check box cleared. 4. Enable and configure the remote base station as follows: a. Disable RF repeat (to stop endless loops over the link). b. Do NOT enable RF linking. Otherwise the analog line will not 86 Network Design TaitNet P25 Conventional System Manual

87 operate. 5. At both ends of the RF link, set the preamble length based on the jitter on the IP link. 6. Decide whether the ends of the RF link will use specific NACs or whether they receive any NAC and transmit the NAC in the voice stream, and program them accordingly. Call Handling The RF link handles calls as follows (assuming a situation with a single base station at the remote site). When the dispatcher makes a call, the main channel group s RF interfaces all transmit it. This is because RF interfaces give it a higher priority than any subscriber calls. The local linking transceiver also transmits the call. When the remote transceiver receives the call, it flags it as coming from the source Dispatcher. The remote base station also transmits the call, because its RF interface also gives dispatcher voice streams priority over any subscriber calls. The result is that the local and the remote channel groups transmit the same signal. Base station Linking transceiver Linking transceiver Base station P25 Console Gateway Source = Dispatcher Remote site Time When the main channel group receives a call from an SU, the RF link handles it in exactly the same way as for a dispatcher call, as above. When the remote base station receives a call from an SU, it can repeat it locally (repeat is enabled) or re-transmit the call after the main channel group has voted on it (repeat is disabled and the link is set up according to Channel Groups with Multiple RF Links on page 92). In either case, the remote linking transceiver transmits it. TaitNet P25 Conventional System Manual Network Design 87

88 The local linking transceiver flags the call as coming from the source subscriber, gives the call an impairment value and sends it to the main channel group. This call information is provided by the local transceiver's configuration. The local transceiver is configured to flag all calls in this way, because the RF link cannot carry voting and switching information. The main channel group also repeats the call from the remote site and provides it to the dispatcher. Base station Linking transceiver Linking transceiver Base station P25 Console Gateway Source = Subscriber Impairment = 7 Remote site Time Understanding and Optimizing RF Linking To understand RF linking and its limitations, it is best to think of the RF link as joining two channel groups (even though one end may be a single TB9100). Voting and selecting occurs at both ends of the RF link. Because the RF link is not as fully featured as an IP link, it has built-in limitations. The RF link cannot pass information in the voice stream that is used for voting and switching. It can only supply an inbound or an outbound stream to the channel group, not both simultaneously, as an IPbased link can in a duplex channel group. A combination of product design, configuration choices, and system implementation is needed to optimize RF linking and ensure a satisfactory solution that minimizes the impact of the limitations of the RF link. The following areas must be addressed. Voice streams The RF link is duplex in the sense that it provides a channel in both directions simultaneously. However, it is an unusual feature of duplex channel groups, that a member may need to provide two voice streams (one 88 Network Design TaitNet P25 Conventional System Manual

89 inbound and one outbound) to the channel group. The RF link cannot support this feature. It can provide the main channel group with an inbound stream or an outbound stream, but not both at the same time. The product design lets you configure the linking transceivers to flag the streams they receive either as coming from a dispatcher (outbound) or from a subscriber (inbound). The voting and selecting of streams that have crossed the RF link is based on this fixed information. On the positive side, the RF link can provide the dispatcher with an SU call while the dispatcher is making a call. If this behavior is desired, the channel groups should be configured duplex. Network delay An RF link adds a delay of 60ms plus the configured preamble duration (usually the minimum of 40ms). With central voting, this additional delay causes no difficulties if there are no voice streams from the local channel group competing for the vote. If the local channel group does produce one or more voice streams, the voice stream from the remote channel group cannot win the vote. It arrives at the central voter too late for skew compensation and is discarded. With distributed voting, the additional delay causes no difficulties if the coverage areas of the two channel groups are disjoint. If they are not disjoint, voting between voice streams from the different channel groups may not be satisfactory due to the additional delay. However, distributed voting can still be a good configuration choice if it is rare for the remote base station and a base station in the channel group to be receiving the same call. Voting The fact that the RF link cannot carry voting and selecting information limits the capability of the system. The result of voting and selecting can sometimes be unexpected. If both channel groups have line interfaces and RF interfaces, voting can give one result at one channel group and a different result at the other. RF linking is therefore not suitable for this situation. If one channel group has a line interface and an RF interface, all streams it sends across the RF link can be flagged as coming from the dispatcher, which means they always are selected in preference to local SU calls. There can be other minor problems as well. For example, if a maintainer uses the control panel microphone at the remote site, that will be selected at the remote channel group but may be selected over SU calls at the main channel group. An RF link works best with the least sophisticated voting type. The voting type should be the same at both channel groups (except in the case of central voting). Switched voting assumes that different streams are from different talkers and does not choose continuously between them. If streams occur at the same TaitNet P25 Conventional System Manual Network Design 89

90 time, the winner is the stream from the base station with the lowest receiver number. Distributed voting re-selects the best stream about five times per second. Because the RF link does not carry signal impairment information, the receiving link transceiver adds a fixed value from its configuration. A low impairment value means that the signal from the link is likely to win most votes. A high impairment value means that the signal is likely to lose most votes. Central voting works least well with RF linking. If the main channel group uses central voting, select switched or distributed voting for the remote channel group. RF repeat Generally, the members of a channel group have RF repeat enabled. They repeat the vote-winning RF signals that they or other channel group members receive. Linking transceivers should generally repeat RF signals that other members of the channel group received, but not ones that they themselves have received, otherwise they would receive and send the same packets in a never-ending loop. When a TB9100 is configured as a linking transceiver, RF repeat should also be enabled. If the Allow loopback box is cleared, the linking transceiver will not transmit voice streams that are marked with its own receiver number. Network address codes There are two main ways of using NACs in an RF link. Use a different NAC for each direction of the RF link. For example, the local transceiver could transmit with the NAC 293 and receive with 283. The remote transceiver would transmit with 283 and receive with 293. In this scenario, the network cannot carry NACs transparently between the SU and the dispatcher. You must use this method if one end of the RF link is a repeater (see Using a Repeater as One End of the Link on page 91). Alternatively, allow the linking transceivers to receive any NAC and transmit the NAC that is in the stream. This allows network designers to distinguish groups of users by NAC but it makes the RF link more susceptible to interference from other P25 systems. 90 Network Design TaitNet P25 Conventional System Manual

91 Using a Repeater as One End of the Link When an ordinary TB9100 base station is used as one end of the link, network designers must take a further step for the link to work properly. Not only must the one remaining linking transceiver not re-transmit signals that have come from the link, it must not accept them and pass them to its channel group either, if they were originally transmitted by the linking transceiver. This can be done using NACs. The linking transceiver transmits a different NAC to the one it receives on. When the base station at the other end of the link repeats the linking transceiver s signal, the linking transceiver does not accept the signal back, because it is configured to receive a different NAC. Accepts 123 (from SU) but not 987 (from linking transceiver) Tx NAC: 123 Base station Linking transceiver Rx NAC: 123 Tx NAC: 987 Base station Rx NAC: Accept any Tx NAC: From stream SUs must be programmed as follows if they are to work with this system. If an SU will be in the coverage area of the remote repeater, it needs to be set up to receive any NAC. This is because (in the current example) it needs to receive locally repeated calls (NAC 123) as well as calls sent over the link (NAC 987). If an SU will be in the coverage of the main channel group, it must be set up either to receive any NAC or to receive the same NAC that SUs at the other end of the link are configured to transmit. (The base stations in the main channel group must transmit only that NAC.) Using a repeater at one end of the link has a further limitation. The repeater cannot distinguish local calls and calls received over the link. Because calls received over the link are likely to have a high signal strength, they may be given priority over local calls that they do not deserve. TaitNet P25 Conventional System Manual Network Design 91

92 Channel Groups with Multiple RF Links A channel group can have more than one remote base station connected over RF and still provide reasonably good voting behavior. Each RF connection uses a pair of TB9100s acting as linking transceivers. The following example shows a main channel group with base stations D, E, F, G, and H and remote base stations A, B, and C. The circles represent coverage areas: these overlap for A and B. Each remote base station has an RF link, provided by a local linking transceiver (LL) and a remote linking transceiver (RL). A RL1 B RL2 LL1 LL2 D Main channel group H LL3 E RL3 C G F When there is more than one remote link, the main channel group needs to vote on signals arriving over a link and to provide the vote-winning signal back across all links. This requires a different configuration from the examples discussed above: 1. The local linking transceiver is allowed to re-transmit signals that it has received from the remote linking transceiver. A signal from a remote base station can then be sent to the main channel group, voted on, and then sent back for repeating. 2. Remote base stations have RF repeat disabled. If the signal they received wins the vote at the main channel group, they receive it back over the RF link and so re-transmit it. If an RF link fails, Task Manager can be set up to enable local repeat in the affected remote base station (for details on setting up the required tasks, contact Tait). 92 Network Design TaitNet P25 Conventional System Manual

93 Configuration settings The TB9100s involved need to have the correct RF repeat and RF linking settings, as shown below. D LL1 RL1 A Main channel group Local site Remote channel group Remote site Configuration D LL1 RL1 A Linking transceiver Disable Enable Enable Disable Link stream source N/A Subscriber Dispatch N\A Link speech impairment Dynamically assigned Select a value between 0 and 15 that is different to the values of other local link transceivers N/A N/A Local loopback N/A Enable Disable N/A RF repeat Enabled or dispatch controlled Enabled or dispatch controlled Enabled Disabled a a. Even though RF repeat is disabled, the remote base station will transmit vote-winning signals received over the RF link. This is because these signals are flagged Dispatch and are treated as if they came from a dispatcher. TaitNet P25 Conventional System Manual Network Design 93

94 5.8 Security Options TaitNet P25 networks provide security protections to guard against unauthorized access to base stations and to CSS functions. The network design needs to specify how these protections should be set up to give the required security while minimizing the inconvenience to users. The CSS is protected by access codes. Base stations and P25 console gateways are protected by password. CSS Access Codes Access codes protect particular CSS functions. Only those with the access code can carry out the function. One access code gives the user Maintainer privileges. These confer the ability to configure and carry out diagnostics on the connected base station. The other access code gives Administrator privileges. These allow the user to change base station passwords and access codes. Without access codes, CSS users can only view CSS screens. They can read a base station configuration but not change it. Access codes can be defined at CSS installation time or at any later time. Base Station Passwords CSS access to a base station or P25 console gateway is protected by password. Generally, the CSS is permitted to remember base station passwords. This means that the user does not need to enter a password each time the CSS connects to a base station. Instead, the CSS authenticates itself to the base station (this is a secure process; at no time can monitoring CSS communications reveal a base station password). Base stations are shipped without a specified password. When connecting to the base station for the first time, you don t enter a password and then you select Element > Change Network Element Password to set the password. This password is stored in the base station. All base stations in a network can be given the same password. If a maintainer becomes untrusted, the Administrator can change the password. The CSS can be instructed not to remember passwords (this is a configuration option at install time). A CSS user must then always enter the password before connecting to a base station. This can only be undone by re-installing the CSS. 94 Network Design TaitNet P25 Conventional System Manual

95 Policy Options The following table shows how the different security policies deal with security risks and summarizes the additional inconvenience involved. Security Risk Security Policy Untrusted Person Gains Access to Product CD Untrusted Person Gains Access to CSS a Maintainer with Access (Potentially Untrusted) b Inconvenience Base station passwords set to default (null password). No access codes for maintainer or administrator privileges. Access is unconstrained. Access to CSS is constrained by privileges Full access Full access Full access None Full access View only access Full access CSS users must enter access codes before carrying out privileged functions. Access to base stations requires passwords (remembered by CSS) No access Access to base stations that the maintainer is responsible for Access to base stations that the maintainer is responsible for Users of each CSS must enter password on first connection to each base station Access requires CSS privileges and base station passwords (remembered) No access No access c Maintainer access to base stations that the maintainer is responsible for. Maintainer cannot change password or access codes. CSS users must enter access codes before carrying out privileged functions. Access requires base station passwords (not remembered) No access No access, even if product CD is also available Access to base stations that the maintainer knows the password for CSS users must always enter password before connecting to a base station Access requires CSS privileges and base station passwords (not remembered) No access No access, even if product CD is also available Maintainer access to base stations that the maintainer knows the password for. Maintainer cannot change password or access codes. CSS users must always enter password before connecting to a base station. They must also enter an access code before carrying out privileged functions a. A CSS should only be able to access a base station if it is within the TaitNet P25 network or the organization s LAN. The firewall must prevent CSS access from the public Internet. b. If a Maintainer without Administrator privileges becomes untrusted, the Administrator can block that maintainer s access by changing base station passwords. c. If untrusted users gain access to a CSS as well as the product CD, they can bypass CSS privileges by re-installing the CSS. The product CD should therefore be stored securely away from any CSS. TaitNet P25 Conventional System Manual Network Design 95

96 5.9 Firewall Where a TaitNet P25 network is connected to an organization s intranet or to the public Internet, a firewall is required to protect the TaitNet P25 network from unauthorized access and to prevent the voice stream from inadvertently being multicast beyond the TaitNet network. The default option is to use the firewall facilities of the central router. The firewall needs to let the following packets through: CSS communications to/from base stations Base station communications to the syslog collector 5.10 Remote Access and Support from Tait To provide the best level of support, it is helpful if Tait engineers can remotely access the TaitNet P25 network. This access can also be made available to dealers if they are providing ongoing support. A TCP/IP connection is required and this enables Tait to do the following: use the CSS to monitor and carry out diagnostic tests on any TB9100 base station on the network. use the CSS to remotely upgrade the base station or P25 console gateway firmware remotely access the base station command line. For this, a secure shell (ssh) session is required. remotely access the router command line. For this, the router must be configured for secure shell (ssh) access and have the IP security feature license enabled. There are two common remote access methods: VPN (virtual private network) via the Internet Dial up modem/router via the public telephone network VPN Access Dial-Up Access Setup cost and effort Moderate Low: no IP infrastructure required Operating cost Low Can be high Performance Broadband speeds (depending on access at customer location) Limited to modem speeds Reliability Good Varies, can be poor Security High High Alternatively, Tait may be able to work with the customer s existing remote access solution. 96 Network Design TaitNet P25 Conventional System Manual

97 VPN Access VPN access creates a secure private tunnel through the public Internet. Cisco VPN server software runs on a Cisco router at the customer s network. Those needing to remotely connect to the network use a Cisco VPN client. Communications via this tunnel are encrypted. Unauthorized access is prevented by firewalls at each end of the link. Pinholes in the firewalls allow access to specific IP addresses and pre-defined ports (those used for the VPN transport). For additional security, customers can unplug the cable connected to the router when remote access is not required. Pinhole Public Internet Pinhole Firewall Router with CISCO VPN server TB9100 Switch Customer LAN or TaitNet P25 network Firewall Tait LAN Tait Support PC running CISCO VPN client Dial-Up Access A modem at the customer site can be dialed from any telephone on the PSTN. Dial-up networking authentication (login/password) is then required to establish an IP connection. Access from a CSS to any base station on the network is protected by the base station password. For additional security, customers can unplug the modem when remote access is not required. TB9100 PSTN Modem Modem Router Switch Customer LAN or TaitNet P25 network Tait Support PC TaitNet P25 Conventional System Manual Network Design 97

98 5.11 Making the Transition to Digital In many cases, installing a TaitNet P25 network involves making a transition from an existing analog system to the new P25 system. This can be done in various ways. Generally, the first step involves adding Tait P25-capable SUs onto the existing system. The transition can be done channel group by channel group; there is no need to change over the entire system at once. The following tables give an overview of some options. Option Step 1 Step 2 Step 3 Transition using P25 dual mode SUs Add Tait P25 SUs (dual mode) onto the legacy base stations Turn off legacy base stations. Turn on Tait P25 base stations (dual mode). SUs transmit analog FM, dispatcher selects analog FM using a function tone. SUs switch to a digital zone. Dispatcher selects digital P25 using a function tone. Transition using analog FM mode Add Tait SUs (analog mode) onto the legacy base stations Turn off legacy base stations. Turn on Tait P25 base stations (analog FM mode) Change Tait base stations and analog gateway to digital P25 mode. Simultaneously, SU users switch to a digital zone. Go straight to digital P25 mode Add Tait SUs (analog mode) onto the legacy base stations Turn off legacy base stations. Turn on Tait P25 base stations (digital P25 mode). Simultaneously, SU users switch to a digital zone Run both infrastructures Add Tait SUs (analog mode) onto the legacy base stations Turn on Tait base stations (digital P25 mode). Continue running legacy base stations. The Dispatch console patches calls between the two systems (either always or as needed). Dispatcher transmits on both systems Turn off legacy base stations once all SUs have switched to a digital zone. Option Advantages Disadvantages Transition using dual mode Provides the smoothest and most gradual transition. Dual mode increases the risk of problems with scanning and voting. Because of dual mode, any user whose radio has not been re-programmed or who does not switch to digital mode can still hear conversations. Dispatch console must be set up to use function tones. Transition using analog FM mode Go straight to digital P25 mode Run both infrastructures Avoids risks associated with dual mode. Dispatch console does not need to use function tones. Lowest risk of performance problems Dispatch console does not need to use function tones. Because of the cross-repeating, any user who does not switch to digital mode can still hear conversations. Users with radios that have not been reprogrammed cannot participate at step 3. Difficult to synchronize the transition, especially if a spare channel is not available. Additional frequencies are required for new base stations. These may need to be purchased for the transition period. False gating at a legacy base station will override digital P25 calls. Patched analog FM calls will appear to digital P25 users to come from the dispatch console 98 Network Design TaitNet P25 Conventional System Manual

99 Using Spare Channels Spare or additional channel frequencies make it possible to carry out a stepwise transition. Set up the spare channel as one of the digital P25 channels, carry out the system acceptance tests on it, and then make the channel operational. When users are ready to begin using this channel, they simply change zone (see Example Plan 1 on page Example Plan 1). In the new zone, the same channel number now specifies the new frequency pair and selects digital P25 mode. Using Zones The best way for users to change from one set of channel definitions to another is by using the zone selector (for Tait mobiles, program the left menu key to call up the Zone menu, so that users can easily change zone). Users continue to use the same channel numbers with the same meanings, but select a different zone for each stage of the transition. This is easier than, for example, remembering to add 6 to the channel number to select the digital P25 equivalent of an old analog FM channel. A final step can reprogram all zones to be the same. This can be done at any convenient time after the transition is finalized. Other Tips Aim to minimize the amount of mobile and portable re-programming. Choose carefully when to install mobiles: recalling the vehicles for reprogramming is to be avoided if possible. Make sure you have an agreed rollback strategy. For each stage in the transition, there should be a procedure for reverting to reliable operation if problems emerge. Changing channel group operation can be done in two ways: by reconfiguring each base station in the channel group using the CSS or by tone remote command from the dispatch console. The CSS method is recommended if the channel is being changed, the tone remote command is recommended if it is only the calling profile that is being changed. (Using tone remote commands to change channel requires setting up Task Manager tasks in each base station in the channel group to propagate the command.) TaitNet P25 Conventional System Manual Network Design 99

100 Example Plan 1 The following example plan is based on the Go straight to digital P25 mode option and proceeds channel by channel. System acceptance tests are carried out on each frequency before it is made available to users. Once a set of users have been assigned to the spare frequency, the old frequency is available for setting up as another new digital channel. The channel numbers continue to mean the same thing for users, but the underlying frequencies change. 1. Add Tait P25 dual-mode radios to the existing fleet. These radios are configured with three zones (three different sets of channel definitions, for selection during the transition period). Users begin operating them on Zone A as part of the existing analog system. 2. While the existing system continues to operate, install Tait TB9100 base stations. 3. Test and commission the first channel group of TB9100 base stations, using the spare frequency pair (F3) and some sample SUs. 4. Users of the Ops frequency switch to Zone B and begin using F3 as their digital P25 channel. 5. F1 is now spare. Test and commission the channel group that uses F1. 6. Users switch to Zone C and the SWAT team begins using F1 as their digital P25 channel. 7. F2 is now spare. Test and commission the channel group that uses F2. 8. Users can now begin using the New channel. This is summarized in the following table. Frequencies Step 1 Step 4 Step 6 Step 8 F1 Ops spare SWAT SWAT F2 SWAT SWAT spare New F3 Ops Ops Ops SU selection Zone A Zone B Zone C (Shaded cells indicate analog FM frequencies, clear cells indicate digital P25.) 100 Network Design TaitNet P25 Conventional System Manual

101 For this plan, the SUs need to be programmed as follows: Channels Zone A Zone B Zone C 1 Ops F1 analog F3 digital F3 digital 2 SWAT F2 analog F2 analog F1 digital 3 New F2 digital Example Plan 2 Here is an example plan for the Transition using dual mode option. 1. Add P25 dual-mode radios to the existing fleet. These radios are configured for dual mode receive and analog transmit. Users can operate them as part of the existing analog system. 2. While the existing system continues to operate, install Tait TB9100 base stations. 3. Test and commission the first channel group of TB9100 base stations, using test frequencies. 4. Cut over to the TB9100 using the existing analog frequencies. Users can be asked to use another channel on the existing system during the brief outage involved. 5. Make some test calls and then begin live operation in analog mode using Tait P25 radios and base stations. 6. After some time of analog operation, ask users to switch their radio to a P25 transmit channel or zone, with dual-mode receive. 7. Repeat steps 2-6 for each channel group until the entire system is replaced by the TaitNet P25 network. TaitNet P25 Conventional System Manual Network Design 101

102 6 Network Management The following describes the use of the CSS (in particular for monitoring channel group voting) and the sylog collector. It also provides an overview of SU numbering. 6.1 Using the Customer Service Software The Customer Service Software (CSS) provides a window into any TB9100 base station or P25 console gateway on the TaitNet P25 network. The CSS is a PC-based program that runs under Microsoft Windows. CSS users can remotely monitor, configure, upgrade firmware, and carry out diagnostic tests. The CSS connects via IP so that it is easy to connect remotely to a TB9100 base station or P25 console gateway. You can run several CSS instances on the one PC and connect each one to a different network element. The following sections show how to use the CSS to monitor a channel group. See also the CSS manual or online Help. 102 Network Management TaitNet P25 Conventional System Manual

103 Monitoring Channel Group Voting The CSS is also able to monitor channel group voting. You can check the voting configuration, see which voice stream is winning and what other voice streams are present. To monitor voting 1. Select Monitor > Channel Group > Status. 2. Connect to a channel group member. If voting is centralized, connect to the central voter as this provides more details. 3. Check the configuration items in the lower table to ensure that the channel group members have a consistent configuration. Receiver numbers should be unique. All members should be on the same channel. All should have the same base station mode. None should be in Standby mode. A network element in Standby mode does not participate in voting. 4. Check that all members of the channel group are present. If a member is absent, its link may be down. 5. In the upper table, look for the green cells in the RF and Line In columns. They indicate which member won the RF vote or was selected. If you are connected to the central voter, data in other rows indicates other voice streams that lost the vote. If voting is distributed, you can only see the winning stream and the stream being received by the member you are connected to. 6. Check to confirm that the voter is operating as expected (see Voting criteria on page 29). TaitNet P25 Conventional System Manual Network Management 103

104 Example Voter Monitoring Displays The voter monitoring display varies, depending on the type of voting (centralized, distributed, or switched), the type of channel group (simplex or duplex), and the member that the CSS is connected to. The following examples are intended to help you correctly interpret the display. Centralized voting, duplex channel group Screens like the following result when the CSS is connected to the central voter. This screen indicates that the Marley s Hill base station is the central voter. The channel group mode is duplex, so that there is voting for the inbound (RF to dispatcher) stream as well as selection of the outbound (dispatcher to RF) stream. Host Name Voting CG mode RF Repeat Rcvr Num RF Rx Type RF Rx Impair Line In Type Line In Src Synch Tx unsync Buffer min (ms) Buffer under % Mt Cass Satellite Duplex True 2 Yes Kainga Satellite Duplex True 3 Yes Mt Cavendish Satellite Duplex True 4 P25 - U FAIL No PWC Satellite Duplex True 5 P25 10 Holdovr Yes Marley s Hill Central Duplex True 1 P25 7 Synch Yes TCL Satellite Duplex True 6 P25 Dig Yes Marley s Hill is the central voter. All others are satellites. Duplex mode means that there are two winning streams, an inbound and an outbound. The green cell shows that Marley s Hill is currently winning the RF vote. PWC is also receiving the call. Its average impairment is higher. Only the central voter can display losing streams. A P25 call from the DFSI at receiver no 6 has been selected as the outbound stream. 104 Network Management TaitNet P25 Conventional System Manual

105 Distributed voting duplex channel group Screens like the following result when the CSS is connected to any member of a channel group with distributed voting. In this case the CSS is connected to the PWC base station. The CSS can only display a vote-losing RF voice stream if the connected base station is receiving the call itself. Host Name Voting CG mode RF Repeat Rcvr Num RF Rx Type RF Rx Impair Line In Type Line In Src Synch Tx unsync Buffer min (ms) Buffer under % Mt Cass Dist Duplex True 2 Yes Kainga Dist Duplex True 3 Yes Mt Cavendish Dist Duplex True 4 Yes PWC Dist Duplex True 5 P25 10 Yes Marley s Hill Dist Duplex True 1 P25 7 Yes TCL Dist Duplex True 6 P25 Dig Yes Duplex mode means that there can be two winning streams Marley s Hill is winning the RF vote. It has the lowest impairment. PWC is also receiving the call A P25 call from the DFSI interface at receiver no 6 has been selected as the outbound stream Simplex operation Screens like the following result when the CSS is connected to the central voter in a simplex channel group. There is only one winning stream. A dispatcher call always wins over any subscriber calls, but you can see any losing RF streams. Host Name Voting CG mode RF Repeat Rcvr Num RF Rx Type RF Rx Impair Line In Type Line In Src Synch Tx unsync Buffer min (ms) Buffer under % Mt Cass Satellite Simplex True 2 Yes Kainga Satellite Simplex True 3 Yes Mt Cavendish Satellite Simplex True 4 Yes PWC Satellite Simplex True 5 P25 10 Yes Marley s Hill Central Simplex True 1 P25 7 Yes TCL Satellite Simplex True 6 P25 Dig Yes Simplex mode means that there can be only one winning stream The central voter sees two RF streams but neither is selected A P25 call from the DFSI at receiver no 6 has been selected as the winning stream TaitNet P25 Conventional System Manual Network Management 105

106 Dispatcher selects and disables receivers Digital dispatch equipment connected via the DFSI can select or disable any receiver in the channel group. Selecting a receiver causes the channel group to declare its signal the vote winner. This also effectively disables all other members. Disabling a receiver excludes it from participation in the RF voting process. When the CSS is connected to the central voter in a duplex channel group, you see a screen like this: Host Name Voting CG mode RF Repeat Rcvr Num RF Rx Type RF Rx Impair Line In Type Line In Src Synch Tx unsync Buffer min (ms) Buffer under % Mt Cass Satellite Duplex True 2 Yes Kainga Satellite Duplex True 3 Yes Mt Cavendish Satellite Duplex True 4 P25 5 Yes PWC Satellite Duplex True 5 P25 10 Yes Marley s Hill Central Duplex True 1 P25 7 Yes TCL Satellite Duplex True 6 P25 Dig Yes Green means that the dispatcher has selected receiver No 5 Red means that the dispatcher has disabled receiver No 1 Marley s Hill is also receiving the call. The central voter selected this call as the vote winner, as instructed by the dispatcher A P25 call from the DFSI at receiver no 6 has been selected as the outbound stream Dispatcher monitors a base station Digital dispatch equipment connected via the DFSI can send a monitor command to the channel group. If a member is in monitor mode, the Mon column displays Monitor. Monitor mode causes the receiver to bypass the normal squelch mechanisms (NAC, CTCSS, or DCS). If the channel group members are configured for collective control of monitor mode, any monitor command will be passed to the channel group. All members will display Monitor. If the CSS is connected to the central voter in a duplex channel group, you see a screen like this when the dispatcher is monitoring the channel (there is an ungated signal that is not outvoted by other signals). 106 Network Management TaitNet P25 Conventional System Manual

107 Host Name Voting CG mode RF Repeat Rcvr Num RF Rx Type RF Rx Impair Line In Type Line In Src Synch Tx unsync Buffer min (ms) Buffer under % Mt Cass Satellite Duplex True 2 Yes Kainga Satellite Duplex True 3 Yes Mt Cavendish Satellite Duplex True 4 P25 -U 5 Yes PWC Satellite Duplex True 5 Yes Marley s Hill Central Duplex True 1 Yes TCL Satellite Duplex True 6 P25 Dig Yes The central voter selected this ungated call. This can only occur if there are no other inbound calls and if the channel group is in Monitor mode. The call will be provided to the dispatcher interface that requested Monitor mode. Monitoring Quality of Service The CSS can display a number of parameters that help you monitor the quality of service being provided by a channel group. The way you monitor varies, depending on whether the channel group is simulcast. There are different links to be monitored: the link from a member to the central voter (A), the link from an external interface (DFSI, trunking, or Failsoft) to the central voter (B), and the link from the central voter to a satellite voter (C). B Central voter A C Satellite voter As there are more voice streams coming into the central voter than going out from it, quality of service issues are most likely at the A link into the central voter. Monitoring Jitter Each time that the jitter on an incoming link exceeds the configured threshold, the QoS jitter alarm is triggered and a counter is incremented. There are two different counters. The local arrival jitter count indicates jitter on packets originating from within the channel group. The remote arrival jitter count indicates jitter on packets originating from outside the channel group. The configured threshold is the Max interarrival jitter (Configure > Alarms > Network Thresholds) and should be adjusted to reflect the jitter in the current network. TaitNet P25 Conventional System Manual Network Management 107

108 To check jitter at the A link Connect the CSS to the central voter and check how rapidly the local arrival jitter count increments. To check jitter at the B link Connect the CSS to the central voter and check how rapidly the remote arrival jitter count increments. To check jitter at a C link Connect the CSS to a satellite voter and check how rapidly both arrival jitter counts increment. The local arrival jitter count monitors the net jitter on the path from a channel group member via the central voter to the satellite voter. The remote arrival jitter count monitors the net jitter on the path from external equipment over the external interface to the central voter and from there to the satellite voter. Monitoring the transmit buffer The CSS displays a number of measures related to the transmit buffer. Jitter may or may not cause buffer underflows, depending on the initial level of signal stored in the buffer. To see basic information for all channel group members, select Monitor > Channel Group > Status. You can see the lowest level that the buffer fell to and the percentage of underflows. To see full details for a single member, select Monitor > Interfaces > Channel Group and view the Transmitter area. This shows you the minimum level of the buffer over the last 5 seconds, the percentage of underflows, and counters for the number of packets that arrived too late to be transmitted because of a buffer underflow. Monitoring synchronized (simulcast) channel groups In a simulcast channel group, monitoring the quality of service focusses not only on the above measures, but more importantly on two additional ones: the late streams count, and the level of the buffer at the furthest member. The late streams count increments when a voice stream arrives later than the transmit time that the central voter requested. The central voter monitors all the transmitters in the channel group and can provide the CSS with the level of the emptiest transmit buffer. The central 108 Network Management TaitNet P25 Conventional System Manual

109 voter is responsible for ensuring that transmitters have enough signal in their buffers and can transmit on time. To monitor QoS in a simulcast channel group 1. Check jitter as described above. 2. Connect to the central voter. Select Monitor > Synchronization > Simulcast and check the Buffer at furthest member box. The contents should be positive. 3. Connect to any member (particularly the most distant member) and check the late streams count (Monitor > Interfaces > Channel Group). 4. If necessary, at the central voter adjust the parameters regulating transmit timing, see Transmit Timing on page Using a Syslog Collector Normally, larger conventional TaitNet P25 networks are equipped with a PC running a syslog collector. (Trunked TaitNet P25 networks use SNMP instead.) A syslog collector is a third-party program that collects, filters, and displays alarm and other messages. These messages come (in the industrystandard syslog format) from Tait network elements (base stations and P25 console gateways) and also from the TaitNet P25 network s switches and routers. The syslog collector makes it easy to monitor and log the behavior of the whole network from one central point. The syslog collector can also be configured to respond if a network element fails. If it does not receive a regular heartbeat message, it notifies the duty technician. Computers running Unix or Linux have a syslog collector as part of their operating system. Windows-based PCs need a suitable third-party syslog collector. Tait recommends the Kiwi Syslog Daemon (see It is able to handle the syslog messages of Cisco routers. The shareware version can be used to explore its capabilities, but the registered version offers useful additional functions such as the ability to display different screens for different base stations. Use the CSS to enable and configure the sending of messages to the syslog collector (Configure > Alarms > Logging). Configure Kiwi Syslog to display and log the messages you are interested in and to filter out unwanted messages. For example, one display can be set up for call records and another for alarms. You can easily switch between them as needed. In addition, Kiwi Syslog can be set up to monitor base station failure. If Kiwi Syslog does not receive a message with the base station s IP address before a timer expires, it carries out the action you specified ( s the technician, pages the technician, or sends a syslog message). In a similar way, Kiwi Syslog can be set up to notify the duty technician when significant error messages are received. TaitNet P25 Conventional System Manual Network Management 109

110 Syslog messages from the base station use the facility code local0 (for base station messages) or local1 (for call records). Tait suggests that routers use the facility code local2 and that switches use local3. The core router can optionally be given its own facility code local4. This enables the syslog collector to efficiently separate messages from different sources. Call Records Each channel group member involved in a call generates a set of records for that call. These can be used to identify the calling and called parties, the type of call and its impairment. If the network element is configured with a logging level of Trace, additional call records are produced that show encryption information and handovers in RF voting from one base station to another. Setting Up Kiwi Syslog to monitor call records You can configure Kiwi Syslog to display only call records and to log them to their own file. You may also want to provide separate displays for each channel group member. To configure Kiwi Syslog for a call record display 1. Select File > Setup and then select Display from the navigation tree. 2. Modify one of the ten display names to Call Records. 3. Add a rule and rename it Call Records 4. Create a filter that allows only call records to pass, as follows. a. Add a filter to the Call Records rule. b. Rename the filter Call Records Only. c. In the Field drop-down list, select Priority. d. Place a tick in each row of the Local1 table. (Call records always have the facility code Local1.) 5. Create an action that displays the filtered call records, as follows. a. Add an action to the Call Records rule. b. Rename the action Display Call Records. c. In the Action drop-down list, select Display. 6. Create an action that logs the filtered call records to a file, as follows. a. Add an action to the Call Records rule. b. Rename the action Log Alarms. c. In the Action drop-down list, select Log to File. d. Define the path and the name of the log file. 7. In the main window, select Call Records from the drop-down list to display call records. 110 Network Management TaitNet P25 Conventional System Manual

111 Interpreting call records In a normal call, you can expect a call start and a call end message. Other call event messages may occur, for example if there is a handover from one base station to another. As call records are quite long, the following examples divide them into two. The first fields in each record provide a local date and time (added by the syslog collector) and the IP address of the sender. The date and time (UTC format) are also included later in the message. (They are provided by the base station. If the base station time is inaccurate, connect to it using the CSS running on a computer with reasonably accurate time; this passes the CSS PC time to the base station, which then corrects its clock to match the PC.) Date Local time Facility code Severity level IP address of message sender Date UTC time IP Module Severity Process address code level generating message Later fields in the record provide information about the call itself. The call start record provides the following information. Call start timestamp (seconds and milliseconds Unique ID of call Call is P25 Call originated at RF interface of reporting base station Not a continuation of a previous call Signal quality measure Priority level of call (not used) Call start record The call end record provides a lot of additional detail about the call. Call end timestamp Call end record Unique ID of call Length of call is 10.1 seconds Call is P25 Caller has ID 9118 Call destination is talkgroup Start NID displays NAC and other information End NID displays NAC and other information Number of LDUs in call Call was encrypted using DES There were no bad voice codewords There were no muted voice codewords Start and end NID The first three digits of the start and end NID display the NAC of the call (293 in the example above). The final digit has the following meaning. TaitNet P25 Conventional System Manual Network Management 111

112 Digit Start NID End NID 7 Call is a TSBK 0 Call is normal 3 Call was a terminator only Call ended normally 5 or A Late entry Call faded BADV and MUTEV BADV indicates the number of bad voice codewords. These are codewords that needed forward error correction. MUTEV indicates the number of codewords that were muted because they had so many errors that forward error correction could not repair them. Values other than 0 may mean that the calling SU was at the edge of uplink coverage. Alarms Each Tait network element (base station or P25 console gateway) monitors a large number of operational parameters. When a parameter value crosses its threshold (some parameter thresholds are built-in, others are configurable), the network element generates an alarm message and (if configured to do so) sends it to the syslog collector. Alarm messages are also stored in the network element s own log, which the CSS can display and save to a file. The CSS can also display the current state of all alarms on the TB9100 it is connected to. Setting up Kiwi Syslog to monitor alarms and other messages You can configure Kiwi Syslog to display only alarms and to log them to their own file. You may also want to provide separate displays for each channel group member. To configure Kiwi Syslog for an alarm display 1. Modify one of the ten display names to Alarms. 2. Add a rule and rename it Alarms. 3. Create a filter that allows only messages with the facility code Local0 to pass. 4. Create an action that displays the filtered alarms on the Alarms display name. 5. Create an action that logs the alarm messages to a file. 6. In the main window, select Alarms from the drop-down list. 112 Network Management TaitNet P25 Conventional System Manual

113 Archiving Log Files Log files need to be archived, otherwise they keep growing in size until they become unmanageable. Kiwi Syslog can automatically archive log files. To set up the archiving of log files 1. Select File > Setup. 2. In the navigation tree, right-click Archiving and select Add new archive schedule. 3. Rename and configure the schedule, for example to archive the logs daily into folders with dated folder names. Example Messages The following sections describe some important messages and give you some assistance in how to identify and interpret them. Only the MSG part of the records are shown. Alarm Standard alarms contain the text FLTLOG, indicating that they are generated by the fault log process. ASF indicates that they originate from the network board. REC indicates that they originate from the digital board. STATE=ACTIVE indicates that the alarm is on. STATE=INACTIVE indicates that the alarm has been cleared. ASF_4_FLTLOG: , 52 - Alarm ASIF_QOS_LOST_PACKETS - STATE=ACTIVE QoS lost packets is the name of this alarm. The CSS manual or online Help provides information about each base station or P25 console gateway alarm. Internal reset You can search the log for messages that indicate that a reset has occurred. First there is a technical message indicating a failure, followed by a message indicating that the base station or console gateway is starting up. REC_0_UNK: , REC_0_NOERROR: $RCSfile: dblm_common.c,v $#00078 ASF_5_MCNTRL: , Mode transition completed to STARTING It is important to distinguish internal resets from resets that were requested by a CSS user. CSS resets generate a message like this: ASF_4_SKSRV: , Base Station reset requested by the CSS Mode transitions When the base station enters Run or Standby mode, a burst of messages indicate the current operating channel and the transmit and receive frequencies: ASF_5_MCNTRL: , Mode transition completed to RUN ASF_5_RXEXIF: , Digital board status: ASF_5_RXEXIF: , Channel: 3 (Valid) ASF_5_RXEXIF: , Tx frequency: Hz TaitNet P25 Conventional System Manual Network Management 113

114 ASF_5_RXEXIF: , Rx frequency: Hz ASF_5_RXEXIF: , Digital board mode: APCO Task Manager actions Each time a Task Manager task is carried out, a message at Notice level is generated. You can search for these using the keyword text. Network board timestamp Timestamp of TM log Keyword text Number of TM task TM timestamp The TM task that has been executed is indicated by a number that is used internally. To find out which task has been executed, count the items in the task list in the CSS, beginning from the top and including any comments, until you reach the task number. Encryption messages If encryption or decryption fails, a message at Warning level is sent. ASF_4_PROTENG: , Cannot decrypt a call with algorithm id 129, key id 3, no license In the unlikely event that the crypto module fails its integrity test, the following message at Warning level is sent....crypto Module Self Test Result:Failed-Restart initiated(2) You need to return the channel module to Tait for repair. CSS activity When a CSS user logs on to a Tait network element, a message is sent only if there is a clock synchronization. ASF_4_SKSRV: , BS clock changing NEWTIME= :50:30Z TIMESOURCE= When the CSS logs off, the following message is sent. ASF_5_SKSRV: , CSS Log Off Request Notifying Base Station Failure Every 15 minutes, TB9100 base stations send a heartbeat syslog message to the syslog collector, provided that they are configured with a heartbeat severity level that is higher than the logging level. The MSG part of this message is like this: , ABS_5_HRTBT: , 0 - Base Station Alarm is INACTIVE in mode Run To set up a syslog collector to respond to base station failure 1. For each base station, set up a rule with a filter for any message from the base station s IP address. 114 Network Management TaitNet P25 Conventional System Manual

115 2. Set up an additional filter with the Field Flags/Counters and the Filter Type Timeout. 3. Configure the filter to become true if a message is not received in 35 minutes. 4. Set up an action to notify the duty technician ( , pager) if the filter becomes true. (If you are using the Kiwi Syslog Daemon, these capabilities are only available in the licensed version.) 6.3 Talkgroup and Individual IDs SUs and dispatch consoles need to be programmed with individual and group IDs. The P25 talkgroup number range is (0x0001-0xFFFF). The full individual number range is (0x xFFFFFF). Of these, are available for general purposes, that is, suitable as SU IDs. If the system has analog dispatch consoles that use MDC1200, these P25 individual and talkgroup numbers need to be mapped to MDC1200 numbers, so that the console can address calls to groups or individuals and display the ANI of calling units. Network elements are provided with a default mapping that is sufficient for networks with up to 1000 SUs. P25 Start Address P25 End Address MDC1200 Start Address MDC1200 End Address Individual Group In P25, individual and group IDs are distinguishable by the number of bits: individual IDs are 24-bit numbers and group IDs are 16-bit numbers. This means that there can be a group number 1 as well as an individual number 1. In MDC1200, group and individual IDs share the one number range. In the default mapping shown above, group addresses have 9000 added to the equivalent P25 group address. If the default mapping is not sufficient for your purposes, you can use the MDC1200 Address Table in the CSS to define additional mappings. If necessary, contact Tait for assistance. If the analog console system uses MDC1200 signaling for supplementary services, there are additional constraints. The console system may not permit the use of MDC1200 numbers that have an E or an F in the hexadecimal version. The P25 equivalent of such numbers should not be programmed into radios. TaitNet P25 Conventional System Manual Network Management 115

116 6.4 Monitoring and Troubleshooting Simulcast Channel Groups Channel groups should be monitored to ensure that they continue to deliver the required level of performance. The Tait Customer Service Software (CSS) includes a wide range of alarm reporting and remote monitoring features to quickly detect changes in system performance. Any subscriber reports of poor coverage should be investigated. However it is important to refer back to the system dossier as they may be reporting problems at locations where the system was never designed to deliver coverage or they may have identified a small area of degraded performance but overall the system still meets the required reliability figure. The diagnostic mode of Tait subscriber units provides valuable tools for investigating such reports. The most likely causes of problems in a simulcast channel group are: Loss of the external reference or 1 PPS signal to a base station. Change in a base station s power output, causing the simulcast capture area to shift, which exposes an area with high delay spread. Drift in a base station s carrier frequency or modulation fidelity, requiring re-calibration. However, there are many other possible factors. Is the problem with the linking network, or a fault at one of the sites or a change to the physical environment in which the system is operating? Problems can be inadvertently introduced: a replacement reciter might not have the correct configuration, or the IP network configuration might have changed, introducing more delay or jitter. It is not possible in this section to list every possible scenario. The goal is to provide some helpful tools and tests that can be used as a starting point to isolate what could be causing problems. For additional help and support please contact your local Tait Dealer or Customer Service Organization. Expected System Performance Simulcast channel groups are designed to deliver a specific audio quality (e.g. a DAQ of 3.4) to a defined area. Achieving this quality throughout 100% of the coverage area is unrealistic due to terrain variation. Typically a figure like 90% or 95% reliability, throughout the required coverage area, is specified as the system requirement. This means when the network is installed there could be a few locations, scattered throughout the coverage area, where the specified audio quality is not met, but the channel groups would still meet the design criteria. When the channel groups are first installed, tests are carried out to ensure the equipment has been installed correctly and that each module is operating within specification. Then a coverage test is carried out. A coverage test 116 TaitNet P25 Conventional System Manual

117 verifies (to an agreed level of confidence) that the required audio quality is delivered throughout the coverage area. A typical coverage test involves dividing the coverage area up into a grid of test tiles and taking a series of samples in each tile. The system dossier for your network may include all this information, providing a comprehensive record of system performance at the time of installation. Routine Maintenance Carry out routine maintenance checks on the base stations in the channel group, to help prevent problems from arising. See the Installation and Operation Manual for details. Relevant Base Station Alarms Regular system maintenance should prevent most faults from occurring. However, if a fault does occur, the system can be configured to generate an alarm. The base station monitors more than 50 alarm conditions. When a condition rises above or falls below a defined threshold, the base station generates an alarm and stores it in its log. Using the CSS, you can view the current status of all alarms (Monitor > Alarms > Status), and a log containing recent alarms (Monitor > Data Logging > System Log). Many alarms indicate a trend towards failure (e.g. High Temperature), although the system will still be operational. You can therefore take corrective action before the system fails. Any alarm should be investigated. Most apply to any type of base station system, but the following alarms are specific to simulcast operation or cause greater problems on a simulcast channel group. Forward power low If the power output from the transmitter at a site drops on a conventional non-simulcast system, this will reduce the overall coverage area of the site. This is also true for a simulcast system, but it may also create problems in other areas. If one site is transmitting a lower power, then in areas where a subscriber unit would normally capture that repeater, it may now have signals of similar strength coming from other sites. The subscribers may now experience multi-path problems, which would show up as areas of poor communication. VSWR high If the antenna or feeder cable at a site is damaged, power can reflect back into the transmitter. This will reduce the transmitted power. The transmitter may also reduce its output power to prevent damage to the final transistors. This will result in similar problems to a Forward power low fault. TaitNet P25 Conventional System Manual 117

118 External reference An external reference is critical to simulcast operation. If the external reference is lost at a site, the transmitter frequency from that site could drift. In the overlap area where the carrier from another other site is still on frequency, the combined signal may not be successfully decoded by the subscriber units. 1PPS pulse and Unsysnchronized The 1PPS pulse is critical for synchronisation. However, if this pulse is lost, a base station will be able to maintain its own synchronisation for a period of time, due to the accuracy of the external reference. Once this (programmable) time period has expired, the base station is considered unsynchronized, since there can no longer be confidence that it is synchronized with the other base stations in the channel group. The base station can be configured either to transmit unsynchronized (and potentially cause problems in the overlap areas), or to stop transmitting altogether. QoS jitter and QoS lost packets If the network is congested or has a poor link, packets could be lost, or excessive jitter could occur. This will create significant problems in the overlap area. Some sites will have the correct data to transmit, and other sites will not, and may have to substitute missing voice packets with silence packets or stop transmitting. Tx not ready Deviation self-calibration is being carried out by the reciter. Monitoring Channel Group Status When diagnosing simulcast systems, the Group Status form (Monitor > Channel Group > Status) is a good place to start. Connect the CSS to the central voter and open the form. You can see all the base stations that make up the simulcast channel group, and quickly identify if one site is missing (perhaps due to a network fault or a problem at that site). In the image below you can see that there are three sites in the channel group, and that Site 1 is acting as the central voter. The top table shows the status of the voting and transmit buffers. You can also see: That a subscriber is transmitting and is being received by two of the three sites, but Site 3 has won the vote. That all sites are synchronized. This column will indicate if a site is in the Holdover period, indicating that it has recently lost the reference but can still be considered synchronized. In this case you should take immediate action, because once the holdover time has ended, the site will become unsynchronized. That Tx Unsynch is false, which means once the holdover period has ended, the site is configured to stop transmitting. The size of the transmit buffer at each site. In this example you can see that the buffer at the farthest site is 32ms, and that there have been no buffer underflows in the last 15 minutes. If buffer underflows are occurring, you may have to increase the Buffer Min setting. 118 TaitNet P25 Conventional System Manual

119 The lower table provides a quick summary of the configuration of each element in the channel group. You can quickly identify that they all have a consistent configuration. Monitoring Synchronization You can see more detailed information about the Synchronization status of the channel group on the Simulcast form (Monitor > Synchronization > Simulcast). This form allows you to see important information, such as how much holdover time is left after a GPS reference has been lost before a site becomes unsynchronized. If you are connected to the central voter, it also shows the marshalling duration being used by the network to achieve the minimum buffer setting at the furthest member of the channel group. If the linking infrastructure s performance has changed and the jitter has increased beyond the level that can be tolerated by the configured buffer minimum setting, subscribers may notice intermittent poor performance, particularly during peak traffic times on the network. TaitNet P25 Conventional System Manual 119

120 Monitoring Network Jitter If buffer underruns are occurring, you may need to increase the minimum buffer setting to overcome the jitter on the network. To understand the extent of the problem, open the Channel Group form (Interfaces > Channel Group). This form displays a summary of the current jitter on the network, as well as a counter that indicates the number of times the maximum jitter threshold has been exceeded. The form also shows the number of packets lost on the network per second or per call. 120 TaitNet P25 Conventional System Manual

121 Monitoring the RF Interface If subscribers are complaining that they can receive, but their transmissions are not being heard, the Channel Group Status form may indicate high impairment from one of the base stations that should have good reception from that location. To investigate this problem further, open the RF Interface form to see a clear overview of the receiver and transmitter performance of the base station that the CSS is logged into. From this form you can quickly verify the received NAC code, signal strength and an estimate of the bit error rate of the signal coming from the subscriber unit. This may indicate that the sensitivity of that site has deteriorated for some reason. You can then use the diagnostic features of the CSS to remotely carry out receiver sensitivity tests, or to sweep the frequency band looking for interfering signals. If subscribers are complaining of poor reception in a particular location, use the RF Interface form to monitor the transmitter performance of the sites that provide coverage in that area. You can monitor the output power from the transmitter and the level of the reflected power coming back from the antenna. The modulation type is displayed along with the source of the signal being transmitted (is it from the local receiver or from another receiver in the channel group). TaitNet P25 Conventional System Manual 121

122 Checking Coverage in the Field If subscribers report poor coverage in a location, and no alarms or network problems are observed using the CSS, the next step might be to go to that location and make a few test transmissions to verify the extent of the problem. A Tait TM9100 or TP9100 subscriber unit has a number of built-in diagnostic modes that can help with this process. In a trunked network, you can carry out these tests using a Tait SU configured with a conventional channel tuned to operate on a traffic channel frequency pair. The trunking controllers can assign the traffic channel to a call at any time, interrupting the test. Measuring RSSI The first test might be to use the Quality of Service (QoS) option. This will display a Received Signal Strength Indicator (RSSI) reading which can be used to verify that the signal strength in that location is correct. If the signal strength is low, it might be an indication that the RF output from one of the transmitter sites is not correct, or that a new building has been erected that is obstructing the signal in that location. Measuring Forward Error Correction The QoS screen also indicates the number of errors in the voice that the vocoder has to correct using Forward Error Correction (FEC). If the display reads 98%, it means that the voice codewords are 98% correct (on average), and this can roughly be translated as a 2% bit error rate. However, to get an accurate measurement of the BER, a known test pattern must be transmitted by the network. This means that the channel must be taken out of service. Sending a test pattern Instead of making test transmissions to measure the quality of the voice codewords, it is possible to use the Tx 1011 option from the diagnostic menu to continuously transmit a test pattern (with NAC 293) from a Tait subscriber unit. This will be repeated through the network and sounds like a 1011Hz tone. You can then use another portable to measure the QoS. You cannot measure BER accurately using this repeated tone, because a P25 repeater changes the status symbols of the test pattern and a residual 1.4% BER will result, even on a good signal. The correct procedure to measure BER is described in Measuring BER below. Measuring BER To accurately measure the BER, carry out a synchronized transmission test. In this test, the channel group transmits a known test pattern. This test should rarely be necessary outside installation and commissioning. Before carrying out the test, you need to isolate the channel group from its site controller. This can be done by changing channel group members configuration to another channel number, which is conventional rather than trunked. It is likely that the members already have such a channel, for use during installation and commissioning. 122 TaitNet P25 Conventional System Manual

123 The test pattern can be transmitted by a single base station (to verify its performance), or synchronously from the simulcast channel group (to verify simulcast operation). To carry out the test 1. Connect to the Central Voter using the CSS and select Diagnose > RF Interface > Synchronized Transmit. 2. Choose whether to transmit the test pattern from just a selected transmitter, or from All transmitters in the channel group. 3. Set the Transmit mode to Tone 1011 and Continuous. 4. Click Start Test. The network will now begin to transmit the test tone. You should be able to hear a 1011Hz tone from the subscriber unit speaker. 5. From the subscriber unit s Diagnostics menu, select the Rx 1011 test. The subscriber unit will now compare the test pattern against a known good pattern stored in memory, and display the BER. If a high BER is displayed, you can move around the coverage area and identify the extent of the problem. Is there just a single location with high BER that could be caused by some local interference? Is there a large area of poor performance that is specific to a particular repeater? Is the area of poor performance in a predicted overlap area between two repeaters? If it is in the overlap area, simulcast design issues could be responsible for the fault. Is the poor performance intermittent or continuous? TaitNet P25 Conventional System Manual 123

124 Finding the Cause of High BER If the synchronized transmission test indicates an area of high BER, you need to ascertain the cause. The multi-path spread value may have changed, the capture boundary may have moved outside the area, or a base station may be poorly calibrated. Investigating Multipath Spread in the Overlap Area If an area of high BER is observed in the overlap area between sites, it is possible that something has caused the multi-path spread value in that region to increase. This means either the power from one of the transmitter sites has changed, or the delay spread value has changed. Delay spread is the difference in arrival time of the same signal from different transmitters. Multi-path spread is proportional to delay spread divided by the power difference between the signals from the different transmitters. The higher the multi-path spread, the higher the BER that will result at the receiving subscriber unit. The modulation scheme used on the network will determine how much multicast spread the subscriber units can handle before the BER exceeds the required quality of service. A simulcast system is designed so that the high delay spread areas occur where the power difference is so great that the multi-path spread value is within the capabilities of the subscriber units. If this is not possible, the launch time of each site can be adjusted to move the high multi-path spread areas to locations where coverage is as important. Checking Launch Time Offsets The delay spread value is determined by the location of the transmitters and the launch time. It is unlikely that a base station has been moved to a different transmit tower, but it is possible that someone has adjusted the launch times. The table at the bottom of the Synchronized Transmit 124 TaitNet P25 Conventional System Manual

125 diagnostic test form provides a summary of the launch time offset set for each site in the simulcast channel group. You can compare this against the values that were specified for each site to ensure the values have not been modified. Checking for the Capture Effect If the area that is showing high BER is supposed to be dominated by one site, you can use the following test to determine if the signal power received from several transmitter sites is similar at that location. 1. Configure a subscriber unit to operate as a narrowband FM receiver on the simulcast system frequency. 2. Identify the repeaters that may overlap in that area. 3. Use the CSS to set them to Standby mode. 4. Use the Transmission Tests form (Diagnose > RF Interface > Transmission Tests) to start a transmit test from each site. Use the following FM settings: 2.5kHz deviation 70% modulation level Set a different modulation frequency for each site (e.g. Site 1 = 400Hz, Site 2 = 640Hz, Site 3 = 1000Hz, Site 4 = 1600Hz). If one site is dominant, you should hear the tone from that site in the location being tested, due to the FM capture effect. If two sites have similar power levels, you should hear frequent changes between the two tones as you move around the overlap area. TaitNet P25 Conventional System Manual 125

126 Remotely Identifying a Faulty Repeater If the BER is high but there are no alarms indicating a catastrophic failure of the equipment at a site, it may be necessary to go to the site and verify the calibration of the equipment. The BER testing so far may have been able to isolate the problem to a single repeater. However, if the problem is in the overlap area, it may be difficult to identify which repeater has the fault. If sites are difficult to access, identifying the faulty repeater remotely could save a lot of time and money. Previous tests have checked the transmitter power and sensitivity of each site using a subscriber unit. However, if this does not identify which repeater is the likely cause of the problem, there are some additional tests that you can carry out remotely if it is possible to connect an antenna to a calibrated radio communication test set (frequency locked to an accurate standard) and receive a transmission from the repeaters. Carrier Frequency Error Check the Carrier Frequency Error from each site by using the Transmission Tests form (Diagnose > RF Interface > Transmission Tests) to start a transmit test from each site individually. Modulation Fidelity (Test 1) Check the modulation fidelity (deviation error) for each site by using the Transmission Tests form to start a transmission. If you have a digital test set, transmit P25. Otherwise use the following FM settings: 2.5kHz deviation 70% modulation level modulate with 30Hz and check that the deviation is 1.75kHz±1% modulate with 1kHz and check that the deviation is 1.75kHz±1% 126 TaitNet P25 Conventional System Manual